Westfield is a city in Plymouth County, Iowa, United States. The population was 123 at the time of the 2020 census. It is the westernmost point in Iowa, this being due to a bend in the Big Sioux River. The nearby Broken Kettle wildlife refuge is one of the few places in Iowa where prairie rattlesnakes are commonly found. Westfield is the purported home town of the central character, Jack Smurch, in James Thurber's 1931 short story "The Greatest Man in the World."