Moorhead is a city in Clay County, Minnesota, United States, and the largest city in northwest Minnesota. It is the county seat of Clay County. Moorhead is located next to the Red River in the Red River Valley. The land around the Fargo-Moorhead area is some of the flattest and richest (for agricultural uses) in the World. This is because it lies on the lake bed of glacial Lake Agassiz, which drained between 9,900 and 11,000 years ago.