Duluth is a major port city in the U.S. state of Minnesota and the county seat of Saint Louis County. Duluth has a population of 86,293 and is the 4th largest city in Minnesota. It is the 2nd largest city on Lake Superior. The largest is Thunder Bay, Ontario, Canada. It has the largest metropolitan area on the lake, with a population of 279,771 in 2010, the second-largest in the state.