At the foundation of this nation, our founding fathers established that the distribution of political power would be governed by both geography and the count of the population. The US Senate dealt with the geography component, so that each state was equality represented in that body by having two members per state. The population component was handled in the US House of Representatives and gave rise to the need for a Census to be conducted each decade. The results of each decennial census would govern the distribution of representative seats to each state. This distribution process is called “apportionment” or “reapportionment”. A history of apportionment can be found on the Census Bureau’s website here.
From the very first allocation of 65 congressional seats in 1789, the number of seats steadily grew each decade until it became frozen at 435 in 1910. That limit was temporarily increased to 437 in 1958 when Alaska and Hawaii were admitted into the Union.
For a history of the number of seats each state has received each decade, click here.
Readers are advised that apportionment is NOT simply dividing the nation’s population by the number of seats, because under the Constitution each state is guaranteed a minimum of one member in the US House of Representatives. With 50 states currently in the Union that means the remaining 385 seats (out of the currently 435 maximum) are apportioned to the states based upon the currently approved formula of equal proportions. See here for a discussion of the formula.
According to federal law and practice the Census Bureau releases state level population counts by December 31 in the year of the Census which become the official counts for reapportionment purposes. These numbers are based on the “total resident population”, including both citizens and non-citizens, for the 50 states. Starting in 1970, the apportionment numbers included U.S. Armed Forces personnel and federal civilian employees stationed outside the United States (and their dependents living with them) that can be allocated back to a home state. Military were not added into the 1980 apportionment numbers, but this was re-instated beginning in 1990 and continues to the current time. The population of the District of Columbia is not included in the apportionment population.
The following are the apportionment results tables done by Election Data Services for each decade since 1940:
Between decades the Census Bureau and others release population estimates and/or projections for state populations. The Bureau’s estimates program generally release data by state at the end of each calendar year, with the data’s base date being set at June 30 of that year. On the other hand, projections look forward to a new date, usually at the upcoming decennial census year. Election Data Services has traditionally projected the Bureau’s census estimates forward to the next decennial census year. Once a decade, generally in the year ending in “5”. The Census Bureau also issues projections for the future, including multiple decades into the future.
The following are past apportionment studies performed by Election Data Services.
Reapportionment Studies (by year)