Census Links is a growing catalog of links to transcriptions of census, tax lists, birth, death, marriage and military records, all freely available to help with your genealogy research.
From the US GenWeb Census Project
Census Index for 1850, 1855, 1860, 1865, and partial 1870 divided by Towns
From the The Ontario County Records and Archives Center
1790 Census, Ontario County, New York
1800 Census, Ontario County, New York