The U.S. resident population includes the total number of people in the 50 states and the District of Columbia. The resident population of the United States on April 1, 2010, was 308,745,538 an increase of 9.7 percent over the 281,421,906 counted during the 2000 Census.
"Apportionment" is the process of dividing the 435 memberships, or seats, in the House of Representatives among the 50 states based on the population figures collected during the decennial census. The number of seats in the House has grown with the country. Congress sets the number in law and increased the number to 435 in 1913. The Constitution set the number of representatives at 65 from 1787 until the first Census of 1790, when it was increased to 105 members.
The first decennial census was conducted in 1790 and has been taken every ten years as mandated by Article I, Section 2 of the U.S. Constitution. Since the first census, conducted by Thomas Jefferson, the decennial count has been the basis for our representative form of government as envisioned by our nation's Founding Fathers. In 1790, each member of the House of Representatives represented about 34,000 residents. Today, the House has more than quadrupled in size, and each member represents about 19 times as many constituents. In 2000, each member of the House of Representatives represented a population of about 647,000.
The apportionment population consists of the resident population of the 50 states, plus the overseas military and federal civilian employees and their dependents living with them who could be allocated to a state. The populations of the District of Columbia and Puerto Rico are excluded from the apportionment population because they do not have voting seats in the U. S. House of Representatives.
The apportionment totals are calculated by a congressionally defined formula in accordance with Title 2 of the U.S. Code.
Read more about the history of Congressional apportionment.