1. Check the Encyclopedia of New York State, Olin Library Reference, F119 .E53 2005 ++
2. Search the catalog for the county as a subject. e.g.,
Tioga County (N.Y) Search by: Subject
Scroll through the subject-headings. Keep in mind that county histories might also discuss the towns within the county.
3. Sear the catalog for historical county atlases and directories
4. Contact/visit local history centers