How the Census Apportions Seats
The method of reapportionment has changed four times in the 229 years following its inception, but the data for it has always come from a decennial national census. The method we use today is known as the Method of Equal Proportions and was first used in 1941. It utilizes a formula that assigns seats based on a priority value until all 435 members are allotted. The number of seats in Congress (435) was set by a federal statute in 1911 and has remained constant – aside from temporary districts for Alaska and Hawaii in 1959. The Census Bureau last allocated Congressional seats on April 26, 2021.