Ipswich is a city in and county seat of Edmunds County, South Dakota, United States. The population was 928 at the 2020 census. Ipswich …Ipswich is a city in and county seat of Edmunds County, South Dakota, United States. The population was 928 at the 2020 census. Ipswich was founded in 1883 as a stop on the Chicago, Milwaukee, St. Paul and Pacific Railroad. It was named after Ipswich, in England, perhaps via Ipswich, Massachusetts.