St. Peter is a city and the county seat of Nicollet County, Minnesota United States. It is 10 miles north of the Mankato – North Mankato metropoli…St. Peter is a city and the county seat of Nicollet County, Minnesota United States. It is 10 miles north of the Mankato – North Mankato metropolitan area. The population was 12,066 at the 2020 census. It is home to Gustavus Adolphus College.