Ulen is a city in Clay County, Minnesota, United States, along the South Branch of the Wild Rice River. The population was 547 at the 2010 census.Near this small community, what is believed to be an authentic Viking sword known as the Ulen sword was found in a field. The sword is currently on display in a museum.Ulen is the southern terminus of the Agassiz Recreational Trail, a 53-mile multi-use trail built on an abandoned railroad grade which has its northern terminus at Crookston, Minnesota.