Historical Population Density by State: 1910–2020 Census Trends and Changes

Population density—the average number of people per square mile of land—has been one of the most revealing measures of how the United States has grown and shifted over the past century. According to the U.S. Census Bureau, the national population density climbed from 26.0 people per square mile in 1910 to 93.8 people per square mile in 2020, while the resident population more than tripled. State-level data show that density has remained highest along the Eastern Seaboard and Pacific coastline and lowest in much of the West, with states such as Alabama rising from 87.8 people per square mile in 2000 to 99.2 in 2020.

Key Numbers

• U.S. population density, 1910: 26.0 people per square mile
• U.S. population density, 2020: 93.8 people per square mile
• U.S. resident population, 1910: 92,228,531
• U.S. resident population, 2020: 331,449,281
• Alabama population density, 2000: 87.8 people per square mile
• Alabama population density, 2020: 99.2 people per square mile
• Alabama density rank, 2020: 29th among 52 jurisdictions (50 states, D.C., and Puerto Rico)
• Density pattern: higher on the Eastern Seaboard and Pacific coastline; lower in much of the West

Explanation

Population density is calculated by dividing the total resident population of an area by its land area in square miles. The U.S. Census Bureau produces density figures for the nation, all 50 states, the District of Columbia, and Puerto Rico after each decennial census. Because land area changes very little over time, increases in density primarily reflect population growth. The national density rose steadily every decade from 1910 through 2020, but the pace varied. The largest absolute increases occurred in the second half of the 20th century, when the post-World War II baby boom, suburbanization, and migration to the South and West pushed more people into previously less crowded areas.

State-level density rankings are influenced by both population size and geographic size. Small states with large populations, such as New Jersey and Rhode Island, have consistently ranked near the top, while large western states with relatively small populations, such as Alaska, have remained at the bottom. The District of Columbia, although not a state, has a higher density than any state because it is a city with a small land area. The Census Bureau includes D.C. and Puerto Rico in its density rankings, which range from 1 to 52.

Understanding historical density helps explain why some regions have more congressional representation, greater infrastructure needs, and different housing patterns. It also highlights the long-term shift of population toward the coasts and the Sun Belt, a trend that accelerated after 1950 and continues today.

Definition

Population density is a measure of average population per square mile of land. It is not the same as population size; a state can have a large population but a low density if it also has a large land area. For example, Alaska has a very small population relative to its enormous land area, giving it the lowest density among states. Conversely, a small state with a moderate population can have a very high density. The Census Bureau uses resident population, which includes all people living in the United States at the time of the census, and land area, which excludes water bodies such as lakes, rivers, and coastal waters.

Historical Data

The table below shows the U.S. resident population and population density for each decennial census from 1910 to 2020, based on Census Bureau data.

National Comparison

The United States as a whole has a relatively low population density compared with many other countries, but the national average masks wide regional differences. The Census Bureau notes that density levels have been higher across the Eastern Seaboard and the Pacific coastline and lower in much of the West. This pattern reflects historical settlement, economic opportunities, and climate. The national density increased by 67.8 people per square mile between 1910 and 2020, a rise of about 261 percent. The largest single-decade increase in density occurred between 1950 and 1960, when the national figure rose from 42.6 to 50.6, an increase of 8.0 people per square mile.

State Comparison

State-level density varies dramatically. The most densely populated states are generally small northeastern states, while the least dense are large western states. For example, Alabama’s density rose from 87.8 in 2000 to 94.4 in 2010 and 99.2 in 2020, keeping it near the middle of the national ranking. In 2020, Alabama ranked 29th among the 52 jurisdictions included in the Census Bureau’s density table. By contrast, New Jersey has long been the most densely populated state, and Alaska has the lowest density. The District of Columbia, with its city-scale land area, has a higher density than any state.

The table below compares Alabama’s density and rank with the U.S. total for the three most recent censuses.

Ranking Table

The Census Bureau assigns density rankings from 1 to 52, including the 50 states, the District of Columbia, and Puerto Rico. A rank of 1 indicates the highest density. The table below shows Alabama’s rank for the 2000, 2010, and 2020 censuses, illustrating how a state’s relative position can shift even as its density rises.

Although Alabama’s density increased in each decade, its rank slipped from 28th to 29th between 2000 and 2010, meaning at least one other jurisdiction’s density grew faster. Between 2010 and 2020, Alabama held its rank at 29th.

10-Year Change

Decennial census data allow direct comparison of 10-year changes. For the United States, population density rose by 7.7 people per square mile from 2000 to 2010 and by 6.4 people per square mile from 2010 to 2020. In percentage terms, the national density increased 9.7 percent in the 2000s and 7.3 percent in the 2010s. Alabama’s density increased by 6.6 people per square mile in the 2000s and 4.8 people per square mile in the 2010s, reflecting slower growth than the national average in the most recent decade.

Year-over-Year Change

Because the decennial census is conducted every 10 years, official population density figures are not available on an annual basis. However, the average annual change within each decade can be estimated by dividing the 10-year change by 10. For the United States, density increased by an average of 0.77 people per square mile per year from 2000 to 2010 and 0.64 people per square mile per year from 2010 to 2020. Alabama’s average annual increases were 0.66 and 0.48 people per square mile, respectively. These annualized figures smooth out year-to-year fluctuations and show a gradual slowdown in the rate of density growth in the most recent decade.

Factors Behind the Trend

Several long-term forces have shaped state population density since 1910. Early in the century, immigration and industrialization concentrated population in northeastern and midwestern cities. After World War II, the rise of the automobile, federal highway construction, and suburban housing developments spread population outward from city centers, increasing density in surrounding counties. Beginning in the 1970s and accelerating through the 2000s, migration to the Sun Belt—especially Florida, Texas, Arizona, and California—shifted density toward the South and West. At the same time, large land areas in the Mountain West and Alaska kept those states’ densities low even as their populations grew. Coastal states continued to attract residents because of economic opportunities, ports, and climate, reinforcing the Eastern Seaboard and Pacific coastline pattern noted by the Census Bureau.

Why It Matters

Population density affects nearly every aspect of public policy and daily life. Densely populated areas require more housing, transportation, schools, and utilities per square mile, while sparsely populated areas face different challenges such as longer travel distances and higher per-capita infrastructure costs. Density also influences congressional apportionment, state legislative districts, and the allocation of federal funds. Understanding historical density trends helps planners anticipate future growth, manage natural resources, and address regional disparities in services and representation.

Limitations of the Data

Population density is an average and can obscure important within-state variation. A state with a moderate overall density may contain both densely packed urban cores and nearly empty rural areas. The decennial census provides a snapshot every 10 years, so it does not capture short-term changes or annual fluctuations. Land area definitions can also affect density calculations; the Census Bureau uses land area rather than total area, which excludes water, but changes in land area due to boundary adjustments or measurement improvements can introduce small inconsistencies over time. Finally, density rankings that include the District of Columbia and Puerto Rico are not directly comparable to rankings of states alone, because D.C. is a city and Puerto Rico is a territory with different geographic and demographic characteristics.

Methodology

The U.S. Census Bureau calculates population density by dividing the resident population from each decennial census by the land area in square miles. Resident population includes all people living in the United States at the time of the census, regardless of citizenship or legal status. Land area excludes water bodies. The density rankings from 1 to 52 include the 50 states, the District of Columbia, and Puerto Rico. The data are published in the Census Bureau’s historical population density tables, which provide figures for every census from 1910 to 2020. The 2020 Census was conducted as of April 1, 2020, and the density figures reflect that date.

Timeline

• 1910: U.S. density is 26.0 people per square mile; population 92.2 million.
• 1950: Density reaches 42.6, reflecting post-war growth.
• 1960: Density passes 50 for the first time, at 50.6.
• 1990: Density reaches 70.4, as Sun Belt migration accelerates.
• 2000: Density is 79.7; Alabama’s density is 87.8, rank 28.
• 2010: Density rises to 87.4; Alabama’s density is 94.4, rank 29.
• 2020: Density reaches 93.8; Alabama’s density is 99.2, rank 29.

Source & Data Date

Primary source: U.S. Census Bureau, Historical Population Density Data (1910–2020), released April 26, 2021, and the Census Bureau’s Population Density of the 50 States, the District of Columbia, and Puerto Rico: 1910 to 2020 table. Data are based on the 2020 Census, conducted as of April 1, 2020, and earlier decennial censuses. Additional context comes from the Census Bureau’s Historical Apportionment Data Map, also released April 26, 2021.