Clontarf is a city in Swift County, Minnesota, United States. The population was 164 at the 2010 census. Clontarf was platted in 1876, and nameā¦Clontarf is a city in Swift County, Minnesota, United States. The population was 164 at the 2010 census. Clontarf was platted in 1876, and named after Clontarf in Ireland, the native land of many of its early settlers. A post office has been in operation at Clontarf since 1876.