Hi Oswego County was made up in 1816 from Onondaga and Oneida Counties. So in 1812 depending on where you are in Oswego County it would fall under one of these 2 Counties. Prior to that 1816 Onondaga was part of Herkimer County. Herkimer was taken from Montgomery in 1791 and Montgomery was previously called Tryon until 1784. Tryon County was taken from Albany County in 1772. Prior to 1798 Oneida was part of Herkimer County until it was named Oneida in 1798. Herkimer was taken from Montgomery in 1791 and Montgomery was called Tryon until 1784 (after the Rev War). Tryon County was taken from Albany County in 1772. Pat R