The U.S. Constitution requires only that the decennial census be a population count. Since the first census in 1790, however, the need for useful information about the United States' population and economy became increasingly evident.
The decennial census steadily expanded throughout the nineteenth century. By the turn of the century, the demographic, agricultural, and economic segments of the decennial census collected information on hundreds of topics. The work of processing these data kept the temporary Census Office open for almost all the decades following the 1880 and 1890 censuses.
Recognizing the growing complexity of the decennial census, Congress enacted legislation creating a permanent Census Office within the Department of the Interior on March 6, 1902. On July 1, 1902, the U.S. Census Bureau officially "opened its doors" under the leadership of William Rush Merriam.
In 1903, the Census Office was moved to the newly created Department of Commerce and Labor. It remained within Commerce when Commerce and Labor split into separate departments in 1913.
For a summary history of the Census Bureau, see Factfinder for the Nation: History and Organization.
For a visual chronology of the history of the census from 1790 to the present, see the Timeline of Census History.
A portable document format version of the timeline is available here.