The first United States census was taken in 1790 and recorded a total population of 3,929,214. A new census has been taken every ten years since that time. For additional information visit the Census Bureau - History site. Included there are features such as an Index of Questions, sections on the various census programs (e.g., agriculture, demographics, economics, etc.), explanations of census geography, and other useful resources.
The Rutgers University Libraries maintain a relatively complete collection of Federal census materials beginning with the 1790 census. The most complete collection is located at Alexander Library (New Brunswick), but additional copies of some materials may be found at the Dana Library (Newark), the Robeson Library (Camden), and other locations. Much of the material is also available online.