Melvin is a city in Osceola County, Iowa, United States. The population was 199 at the time of the 2020 census. Melvin had its start in the ye…Melvin is a city in Osceola County, Iowa, United States. The population was 199 at the time of the 2020 census. Melvin had its start in the year 1900 by the building of the Gowrie branch of the Rock Island Railroad through that territory.