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Historical Apportionment Data Map
Historical Apportionment Data Map
This interactive tool enables users to view more than 10 decades of apportionment and population data.
Data Tables
Notes for Population Map
The population change and population density data are based on the resident population counts from each decennial census, which include all people living in the United States at the time of each census.
Population change is the rate of change in population between decennial census years.
Population density is a measure of the average population per square mile of land. Density rankings of 1 to 52 include the District of Columbia and Puerto Rico.
Notes for Apportionment Map
Apportionment is the process of distributing representatives (or seats) in the U.S. House of Representatives among the 50 states based on the apportionment population counts from the decennial census. The District of Columbia and Puerto Rico are not included. The apportionment population count for each state is not always the same as its resident population count. For more information, see Historical Perspective.
Population per representative is calculated by dividing the apportionment population count by the number of representatives.
The "United States" value for "Change in Seats" indicates the total number of seats that were reassigned (i.e., shifted from one state to another) that decade, except for the 1910 value, which indicates the number of seats that were added to the U.S. House of Representatives since 1900.
Alaska and Hawaii gained statehood in 1959. Arizona and New Mexico gained statehood in 1912. For apportionment, data before those periods are not reflected on the map.
In 1920, the apportionment counts were transmitted to Congress, but Congress did not reapportion that decade.
Related Information
Congressional Apportionment
Information about congressional apportionment for the current and past Decennial Censuses.
Decennial Census of Population and Housing
The U.S. census counts every resident in the United States. It is mandated by Article I, Section 2 of the Constitution and takes place every 10 years.
Tutorial
How to Access and Visualize 2020 Census Apportionment Results
This Data Gem will teach you how to access and visualize apportionment results using the Historical Apportionment Map.
Page Last Revised - April 21, 2023
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