As mandated by the U.S. Constitution, our nation gets just one chance each decade to count its population. The U.S. census counts every resident in the United States. It is mandated by Article I, Section 2 of the Constitution and takes place every 10 years. The data collected by the census determine the number of seats each state has in the U.S. House of Representatives (a process called apportionment) and is also used to distribute billions in federal funds to local communities.