Check the 1860 census index, when you locate the town or city, check the
1865 NYS census for that town, this will tell you the county in NYS or the
State where the parents were born. You might TRY a gamble that Jefferson Co.
might have a marriage record altho NYS didn't mandate them until 1880. If
you can tell the town, they may have older records. Good luck! PS Have you
looked for printed genealogies of the Stilwell/Stillwell family?