St. Johnsville is a town in Montgomery County, New York, United States. The population was 2,631 at the 2010 census. Accounts vary as to the etymology of St. Johnsville, but most of them state that the town and its village are named after an early surveyor and commissioner, Alexander St. John. Still others credit the naming of St. Johnsville to a former name for the area, St. John's Church. The Town of St. Johnsville is in the northwestern part of the county.