Three Rivers is a city in St. Joseph County, Michigan. The population was 7,973 at the time of the 2020 census. Three Rivers derives its name from its location at the confluence of the St. Joseph River and two tributaries, the Rocky and Portage rivers. The St. Joseph River flows into Lake Michigan. The city is the home of St. Gregory's Abbey, a Benedictine monastery of the Episcopal Church, which was established in 1946.