(Yates Co. Historian, Frances Dumas.) Their url is: http://www.yatescounty.org/upload/12/historian/genweb.html . You can always get to it from our unyg.com website by clicking on "NY Counties & Census" then click on the "Yates" county name.
Yates County was formed in 1823 and from the unyg website you will notice that their county clerk has some of the New York State Census for 1825, 1835, 1845, 1855, 1865, 1875, 1892, 1915 and 1925. See some of my previous Blogs regarding the NYS Census, http://ny-genes.blogspot.com/2007/02/new-york-state-census-1825-1835-1845.html
The Yates Co. GenWeb page has a great list of very unusual items available, and information on how to send for photocopies. Here is a partial list; Civil War service Records 1861-1865, Some of the early town record books for Jerusalem, Benton, Barrington, Stanley, Potter, Milo, and some early Village of Penn Yan Tax Records. There are also some early church records.
They also have Indexes to some early Deeds and Mortgages that were transferred from their parent counties of Ontario and Steuben. Marriage record Indexes 1908-1935 (see UNYG Blog: http://ny-genes.blogspot.com/2006/11/new-york-state-marriages-1908-1935.html)
There is an "every" name index to Yates County Surrogates Records, 1823-1910, and early Surrogates Packets. There is a newspaper index, some military records for the War of 1812, Civil War, and WW I. They also have an all name index to Cleveland's 1873 "Yates county History." Plus lots of links to other sites of interest.
This is a first rate website that should be very helpful to anyone researching in that gorgeous area of the Finger Lakes.
Upstate New York Genealogy