Sheffield is a city in Franklin County, Iowa, United States. The population was 1,130 at the time of the 2020 census. Sheffield was platted in 18…Sheffield is a city in Franklin County, Iowa, United States. The population was 1,130 at the time of the 2020 census. Sheffield was platted in 1874, and it was named for a personal friend of the founder's. Sheffield was incorporated in 1876.