Ossian is a city in Winneshiek County, Iowa, United States. The population was 802 at the time of the 2020 census. Ossian was platted in 1855. …Ossian is a city in Winneshiek County, Iowa, United States. The population was 802 at the time of the 2020 census. Ossian was platted in 1855. It was named for its founder, John Ossian Porter. Ossian is located at 43°8′47″N 91°45′50″W / 43.14639°N 91.76389°W.