Willow River is a city in Pine County, Minnesota, United States, at the confluence of the Kettle and Willow Rivers. The population was 415 at the 2010 census.

Pine County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 28,876. Its county seat is Pine City. The county was formed in 1856 and organized in 1872. Today, Pine County is the fastest growing county in the state.