Tennant is a city in Shelby County, Iowa, United States. The population was 78 at the time of the 2020 census. Tennant had its start in 1903 …Tennant is a city in Shelby County, Iowa, United States. The population was 78 at the time of the 2020 census. Tennant had its start in 1903 by the building of the Chicago & Great Western Railroad through that territory.