Starting with the 1990 Census, the majority of the census data is posted online on the U.S. Census Bureau's site, Census.gov. The data is available not only for viewing but can also be manipulated. Accessing the data is done through the interfaces "American Community Survey" and "American FactFinder" listed below.
Other sites also have current Census data available and are also listed below.
Data from the historical censuses was naturally released in print format. The sites listed below provide online access to these volumes. If the data you're looking for is not available on these sites, the Library has print copies of most of the volumes of all of the ceususes. To find them, do a keyword search in the catalog by the specific census, e.g. "1910 Census" or "Sixteenth Census".
This work is licensed under a Creative Commons Attribution 4.0 International License.