Reynolds v. Sims
Every ten years since 1790, the United States has conducted a census as authorized by the Constitution. This is far more than a simple headcount; census data provides a detailed national portrait which assists the federal, state, and local governments (and private entities, who also access the information) in demographic-based planning. The Census Bureau distributes detailed questionnaires to households, and the cumulative answers help to determine not only population, which governs the apportionment of representatives at the state and federal levels, but other trends that will influence policy in areas that range from education to the building of interstate highways.
Determining apportionment remains the primary constitutional purpose of the census, and Congress has oversight as to the form and method of the count. Federal marshals were the first census takers, but by 1880 it became necessary for the Census Bureau to hire legions of employees. Since 1970, the census has been by mail. By 1990, critics charged that the mail-based census might not be effective enough, given the existence of a homeless population largely outside its reach.