Chapin is an unincorporated community and census-designated place in northern Franklin County, Iowa, United States. It lies along local roads just off U.S. Route 65, north of the city of Hampton, the county seat of Franklin County. Its elevation is 1,155 feet, and it is located at 42°50′1″N 93°13′20″W. Although Chapin is unincorporated, it has a post office with the ZIP code of 50427, which opened on 29 February 1860. As of the 2020 census, its population was 71.