Digitized and Searchable Historical Census Bureau Publications via the Internet Archive
The Internet Archive brings together the digitized government publications from lots of different projects so that you can search in one location for historical publications containing statistics. Of course, the search isn't exhaustive since not everything has been digitized, but the depth increases every day and there are materials from the Census back to at least the first decade of the 20th Century. Check it out at http://www.archive.org/search.php?query=creator%3A%22United%20States.%20Bureau%20of%20the%20Census%22.