The Top 6 Population Migrations in American History

US Population Over Time
Population Per Square Mile by County

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Source: US Census Bureau populations 1790-1990, 2000, and 2010

Timeline of Major Migrations

How the Midwest Was Won
1790 to 1840


At the dawn of the 19th century, the bulk of the U.S. population was consolidated in a handful of states along the East Coast, from South Carolina to Maine. By the middle of that century, the U.S. map started to look much more familiar to modern Americans, as several events pushed the population westward and toward cities.

The Louisiana Purchase in 1803 had dramatically increased the overall size of U.S. borders, but travel was still perilous and time-consuming. And while the economy, thanks to the Industrial Revolution, was beginning to become less agrarian, it still was overwhelmingly tied to farming. A second military conflict with Great Britain, the War of 1812, sparked a surge of western settlement, and the development of railroad systems made long-distance travel possible for more people.

By 1840, many former population centers on the East Coast began to see population declines as what we know as the Midwest began to take shape.

The Gold Rush, Great Lakes, and the Great American Railroad
1830 to 1860


When the Erie Canal opened for business in 1825, travel time between Albany and Buffalo dropped from two weeks to just five days. At the time and perhaps still considered one of the most successful public projects in American history, the canal's opening sparked incredible growth throughout the entire Great Lakes region, which became heavy with industry and agriculture. Population centers like Chicago, Cleveland, and Detroit swelled, as did their surrounding areas.

Just under 20 years later, the West Coast found itself seized by gold fever, as James Marshall's discovery of the precious metal at Sutter's Mill ignited years' worth of mass migration to California and other western states. By 1855, seven years after Marshall's find, it's estimated that at least 300,000 people had arrived in California from all around the world. About half the people who ventured to California were Americans, and many of them, instead of attempting a perilous over-land trek across the continent, opted to travel by sea, making it a six-month-plus journey.

Though it would come too late for the 49ers who made their trek during the initial Gold Rush, construction of a transcontinental railroad revolutionized coast-to-coast travel. Railroad production was in full swing during the first half of the 19th century, as about 9,000 miles of track had been laid by 1850. The Pacific Railroad Act of 1862 tasked two companies, the Central Pacific and Union Pacific, with constructing a transcontinental railroad, finally culminating in the route's completion in 1869. Before the railroad was completed, a cross-country journey cost nearly $1,000; when the tracks were complete, the cost dropped to just $150.

The net effect of all three major events saw enormous population growth in California and the Great Lakes area.

"Civil wars leave nothing but tombs" - Alphonse De Lamartine
1860 to 1870


By the time the last shots were fired and the final confederate soldiers had surrendered, as many as 750,000 lives were lost in Civil War fighting. That incredible number represents about 2 percent of the overall U.S. population at the time, making it by far the deadliest conflict in American history, accounting for more deaths than all other wars combined. About 1 in 4 soldiers who went off to war never returned.

In addition to the human toll, the war wrought enormous demographic changes, as much of the wealth that had existed in the South, generated by years' worth of labor by enslaved people, was destroyed. Reconstruction, implemented by Congress from 1866 to 1877, was designed to reintegrate the former confederate states into the union, but for many it had the opposite effect.

While Reconstruction saw millions of newly free African-Americans participate in political and civil life, buy lands, reunite with families, start schools and businesses, and elevate their stations in life, it also set the stage for the Jim Crow-era laws that would soon be enacted all over the South. Thousands of African-Americans simply left the South altogether, many of them heading West, often on foot.

In Plains Sight: The Homestead Acts
1860 to 1900


The Homestead Act of 1862 and subsequent homestead measures aimed to open public lands to individual farmers, or homesteaders. By 1900, settlers had claimed 80 million acres of land through these provisions, forcing Native American tribes off their lands and onto reservations.

Most of the land was west of the Mississippi River, and eventually nearly 10 percent of the total U.S. landmass was given to the 1.6 million homesteaders who participated. The Homestead Act of 1866, in particular, while ineffective in general, did achieve at least part of its goal: The act is credited as being partially responsible for enabling one-fourth of southern black farmers to own their land by 1900.

The first transcontinental railroad was completed in 1869, and by the end of the century, the United States was home to more than 200,000 miles of railroad track and a total of five transcontinental lines, making travel across the vast continent feasible for millions, and population growth on the Plains.

The End of Native America, and the Oklahoma Land Rush
1890 to 1910


By definition, migration of Americans has typically meant displacement of native tribes. In fact, every entry on our list so far has seen American populations move at the expense of tribal communities. But the Dawes Act of 1887 was a particularly insidious piece of legislation. On its surface, it provided Native Americans a portion of land that formerly was tribal land, in addition to American citizenship. But the effect was utterly devastating to tribal populations. By 1900, the amount of land in native hands plummeted from 150 million acres to just 78 million.

The 1889 Indian Appropriation Act opened nearly 2 million acres of former tribal land, ceded to the U.S. government by the Muskogee and Seminole tribes after the Civil War, for settlement under the 1862 Homestead Act. Precisely at noon April 22, 1889, thousands made a mad dash on foot, in wagons, or on horseback to claim the rich agricultural land in Oklahoma.

As Harper's Weekly put it at the time, the results were incredible: "At twelve o'clock on Monday, April 22d, the resident population of Guthrie was nothing; before sundown it was at least ten thousand. In that time streets had been laid out, town lots staked off, and steps taken toward the formation of a municipal government."

The American Love Affair With Cars and Air-Conditioning
1900 to 2010


Five years after Henry Ford introduced his Model T car, American automakers produced 80 percent of all the cars in the world. By the time Ford stopped making the Model T in 1927, the automobile had gone from a luxury item to something within reach for the average American family.

If the history of American migration in the 19th century is a story told on horseback, then the 20th century's story is undoubtedly gas-powered. Cars allowed cheap and easy movement, which enabled cross-country relocation. Americans' love of cars necessitated construction of a massive, coast-to-coast highway system. And cars continue to support the urbanization and suburbanization of America.

In the middle of the 19th century, only 11 percent of Americans lived in cities, and suburbs weren't even a thing yet. By the 1960s, less than a third of Americans lived in rural areas, more than 60 percent lived in cities, and an emerging 8 percent lived in suburbs. To better understand just how consolidated the US has become, visualize the US population in 3D.

Just as the past half-century has seen population grow in major cities, warm-weather states have also seen their ranks swell. One possible reason, other than the car? Air-conditioning. In 1902, a young engineer from New York, Willis Carrier (yes, that Carrier), invented the first modern air-conditioning system. Use of AC soon spread to department stores, offices, and train cars. But residential use lagged, likely owing to cost and the bulkiness of AC units; in 1965, just 10 percent of homes had air-conditioning. Today that number is nearly 90 percent.

Maps of Population Change by Decade

For those wanting to dig deeper into the data and to look for other smaller changes, we have prepared maps of the population changes for each decade.

Regional Population Differences

US Regions

Percent of US Population by Region


The Civil War devastated the South on a human and financial level. Before the war, the South historically boasted around half the population, and even as the Midwest and the West began to grow, the South still held the most population of any region. The Civil War changed things for nearly eight decades.

Today, though, the South again has regained its position as the population center of the United States. Thanks to growth in several key states, including Texas, Virginia, and Florida, the South today boasts nearly 40 percent of the American population, while the Northeast has seen its population decline from about 50 percent of the total in the 19th century to just 18 percent today.

Top 10 Highest Population Counties Over Time

1790

Albany, NY
75,736
Charleston, SC
66,985
Hampshire, MA
59,681
Essex, MA
57,913
Worcester, MA
56,807
Philadelphia, PA
54,391
Dutchess, NY
45,266
Suffolk, MA
44,875
Rockingham, NH
43,169
Middlesex, MA
42,737

1900

New York, NY
2,050,600
Cook, IL
1,838,735
Philadelphia, PA
1,293,697
Kings, NY
1,166,582
Allegheny, PA
775,058
Suffolk, MA
611,417
St. Louis city, MO
575,238
Middlesex, MA
565,696
Baltimore city, MD
508,957
Cuyahoga, OH
439,120

1950

Cook, IL
4,508,792
Los Angeles, CA
4,151,687
Kings, NY
2,738,175
Wayne, MI
2,435,235
Philadelphia, PA
2,071,605
New York, NY
1,960,101
Queens, NY
1,550,849
Allegheny, PA
1,515,237
Bronx, NY
1,451,277
Cuyahoga, OH
1,389,532

2010

Los Angeles, CA
9,818,605
Cook, IL
5,194,675
Harris, TX
4,092,459
Maricopa, AZ
3,817,117
San Diego, CA
3,095,313
Orange, CA
3,010,232
Kings, NY
2,504,700
Miami-Dade, FL
2,496,435
Dallas, TX
2,368,139
Queens, NY
2,230,722

The Most Interesting Population Changes

Current Top 5 Most Populated

The five most populous U.S. counties each contain one of the 10 largest cities in America. Most of those cities are relatively young, however. The largest county on the list, Los Angeles, began to see its population surge around 1930, while Chicago (Cook County), the second-largest, saw steady growth beginning in the 1840s. The others, San Diego, Houston (Harris County), and Phoenix (Maricopa County) all have seen huge gains since the 1970s.

New York City

Though it wasn't the first-ever American city, by the time of the first constitutionally required U.S. Census in 1790, New York City was the largest city in the young nation and has remained America's largest city since.

Way back then, the population was just over 33,000. Today the population of the five boroughs tops 8 million. For more than a century, Manhattan (New York County) was the most populous borough until it was surpassed by Brooklyn (Kings County) in the 1920s. Today, both Brooklyn and Queens are larger than Manhattan, which until 1914 contained the land that would become Bronx County.

New York's five boroughs have a total of just 302 square miles; the sheer population density naturally forced people to surrounding areas. Three of the four most populous New York metro area counties outside NYC today have populations nearing 1 million each, and combined, the four counties (three in New Jersey and one in New York) boast more than 3.2 million inhabitants. Between 1900 and 1930, each of the counties saw rapid increases in their populations. As New York City itself has grown, its very large suburbs have grown as well. In fact, each of the four suburban counties are larger (in some cases, by about double) than the borough of Staten Island (Richmond County).

Charleston, SC (1886 Earthquake)

Late in the evening Aug. 31, 1886, a 7.3-magnitude earthquake struck the city of Charleston, South Carolina. The quake was so severe, that outside the immediate area of the tremors, there was speculation that Florida had broken off North America. Sixty people were killed, and the structural damage was estimated to be as much as $6 million.

In 1880, the population of Charleston County was 102,800; by 1890, four years after the quake, the population had plummeted by more than 40 percent to just 59,903. Charleston has seen a resurgence in recent years, jumping by about 110 percent since 1950.

Loss of Coal Mines (1940s and 1950s)

Though they're often used as a political tool by candidates and activists on all sides of the issue, the loss of coal mining jobs in the U.S. has shaped the demographics of the largest counties of the Coal Region in Pennsylvania.

Coal replaced wood as the primary energy source in the U.S. in the 1880s and remained the largest source of energy until the 1950s, when petroleum exceeded coal. Employment in the U.S. coal industry peaked in the 1920s, then around 900,000 people were coal miners; the numbers have continued to decline since then.

The population of the Coal Region of Pennsylvania reflects the collapse of the coal industry. The population of the three largest counties surged by a combined 184 percent between 1880 and 1930. Since 1940, the population of those counties has declined by more than 29 percent.

Silicon Valley (1960 to present)

Today the center of the computing world, until the 1930s, Silicon Valley was powered by the radio and telegraph industries thanks to San Francisco's port. The influence of Stanford University helped make the area a research center, and in 1939, Hewlett-Packard was established in Palo Alto. The term "Silicon Valley" wouldn't be coined for another 30 years, but Silicon Valley was well on its way to becoming the epicenter of the tech world.

Companies like Apple, Oracle, and Atari were founded in the valley in the 1970s, Yahoo, PayPal, Google, and eBay joined in the 1990s, while more modern companies liked Facebook, Uber, and Tesla since made their homes in Silicon Valley.

Since the term was first popularized in the early 1970s, the counties that make up Silicon Valley have seen their population rise by a collective 63 percent. Zoning restrictions in place since the 1960s have limited the housing supply in San Francisco and the rest of the Bay Area, increasing demand and prices, and those restrictions, combined with multiple tech booms in the broader Silicon Valley area, make it one of the most expensive places in the U.S. to buy a home today.

Rust Belt (1970 to 1990)

The rise of manufacturing helped build cities like Buffalo, Chicago, Cleveland, Detroit, Philadelphia, Pittsburgh, and others. A flourishing manufacturing sector led to nicknames for such regions as "Manufacturing Belt," "Factory Belt," or "Steel Belt." As U.S. manufacturing began undergoing steep declines starting in the 1970s and 1980s, such cities began to be called "Rust Belt" cities.

Outside of Cook County, the home of Chicago, the major Rust Belt counties, particularly Wayne County (Detroit), have seen steady declines in their populations since the 1970s. The combined population of Philadelphia County, Allegheny County (Pittsburgh), Wayne County (Detroit), Cuyahoga County (Cleveland), and Erie County (Buffalo) has dropped by 25 percent since 1970, while Cook County (Chicago) saw consistent rises and falls since 1960 and has gone up just 1 percent overall since then.

Orleans Parish, LA (2005 Hurricane Katrina)

A tropical wave coalesced with the remnants of a tropical depression around Aug. 23, 2005, over the Bahamas. Early the next day, the storm, headed westward toward Florida, intensified into Tropical Storm Katrina. The storm strengthened into a hurricane a mere two hours before it made brief landfall in the Miami area on Aug. 25, before pushing back out into the Gulf of Mexico. Sucking up the warm waters of the gulf, Katrina rapidly intensified into a massive Category 5 storm.

By the time it made its second landfall on Aug. 29, the now-Category 3 storm crashed into Gulfport, Mississippi, devastating the coastal town. The rain, winds, and storm surge overwhelmed levees and floodwalls in New Orleans, flooding 80 percent of the city and neighboring parishes. As the remnants of Katrina continued moving across the United States, it continued causing destruction in states far from the Gulf of Mexico.

Nearly 2,000 people died in seven states, and as many as 66 are still missing to this day. The economic toll topped $125 billion, making Katrina by far the costliest Atlantic hurricane at the time. The environmental effects were devastating as well, as the storm surge led to beach erosion, destruction of marshes, and oil spills.

Widespread relocation of hurricane refugees helped push Orleans Parish's population down by nearly one-third between 2000 and 2010. While the city has seen population growth since then, more recent estimates still put the population below 2000 levels.

Research the Historical Population of US Counties

Learn about the historical population of your county plus housing data, economic health indicators, and more. Use the search box above to research thousands of counties across the US.

What about boundary changes?

Whenever possible, the US Census Bureau attributed the population to what is considered the present-day location of various counties. They have extensively recorded the various changes in geography over time.

Only 22 of over 3,100 counties that are listed in the census data no longer exist. These 22 counties are not included in the map. These counties are primarily in Alaska and Virginia. The remainder of the 22 are located in Campbell, GA; Milton, GA; Yellowstone National Park; and parts of South Dakota.

State (dark gray) and territory (light gray) boundaries are shown over time. Because the census was typically taken during the summer, state and territory boundaries are shown as of June of each census year. Thanks to Lincoln Mullen for making his work on historical boundaries available.

Who is included?

Only those included in the US Census are reported. It wasn't until the 1900 census that what is now the entire US was included. Prior to 1890, American Indians were not included unless they lived in settled communities. Their inclusion was long after the forced migrations (Indian Removal Act and the Trail of Tears) that occurred during the early 1800s.

Slaves have been counted during the census since it began in 1790 and are included in population totals. However, they were not counted entirely for legislative representation or taxation due to the Three-Fifths Compromise of 1787. It wasn't until the Fourteenth Amendment in 1868 that repealed the Compromise that all persons except Indians not taxed were included in population totals used for representation and taxation.

Data Sources

Much of the data comes from work done by the US Census Bureau in the 1990s. We have combined that data with numbers from 2000 and 2010. For those looking to do further research, we are making available the historical counties' and the historical states' population numbers. The linked format includes the latest 2000 and 2010 numbers as well as being in a format that should be easier to work with than the original Census Bureau source.