Every 10 years, the U.S. Census Bureau conducts a census to determine the number of people living in the United States. The U.S. Census Bureau conducts the census in years ending in zero, on Census Day, which is April 1.

The data collected by the decennial census are used to apportion the number of seats each state has in the U.S. House of Representatives.  The first U.S. census was in 1790 during the first term of our first president, George Washington. Secretary of State Thomas Jefferson led the effort. The population was 3,929,625, and Congress used these results to apportion 105 seats among 15 states.

The Constitution of the United States, Article I, Sections 2 and 9, directs that a census or enumeration be taken.

Section 2 states, “The actual enumeration shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent term of ten years, in such manner as they shall by law direct."

In 1954, Congress codified earlier census acts and all other statutes authorizing the decennial census into law under Title 13, U.S. Code. Title 13 requires the Census Bureau to notify Congress of the planned subjects for the census no later than three years before that census, and of the specific wording of questions to be asked no later than two years before that census.

Apportionment is the process of dividing the seats in the House of Representatives among the 50 states based on the population figures collected during the decennial census. The U.S. Constitution mandates that an apportionment of representatives among the states must be carried out every 10 years. Therefore, apportionment is the original legal purpose of the decennial census, as intended by our Nation's Founders. 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, Article I, Section 2 states, “Representatives and direct taxes shall be apportioned among the several states which may be included within this union, according to their respective numbers.”

Redistricting is when state officials redraw the boundaries of the congressional and state legislative districts in their states after each census. This accounts for population shifts since the last census.