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.
Current Apportionment and Recent Trends
The Census Bureau last allocated Congressional seats on December 21, 2010.
Reapportionment sent 11 seats from the Northeast and Midwest to the South and West in 2010.
Ten years earlier, a similar 10-seat transfer occurred. The changes so far in the 21st Century have resulted in New York losing 4 members, Ohio and Pennsylvania each losing 3, and Michigan and Illinois both dropping 2. Over the same period, Texas increased by 6 members, Florida by 4, Arizona and Georgia by 3 each, and Nevada by 2.