Greenfield is a city in and the county seat of Adair County, Iowa, United States. As of the 2020 census, the city population was 2,062. The ar…Greenfield is a city in and the county seat of Adair County, Iowa, United States. As of the 2020 census, the city population was 2,062. The area surrounding Greenfield was settled in 1854. The plan for the town of Greenfield was designed in 1856, after Milton C. Munger purchased the land that the town would be built on. Munger is responsible for the design of Greenfield's unique Lancaster-style town square, and the city park located at Grant and NE Second Street was also included in the original plat. Greenfield is named after Greenfield, Massachusetts. Greenfield became the county seat in 1875, after battling out nearby Fontanelle for the title. The city was incorporated on May 22, 1876.