St. Joseph County, colloquial St. Joe County by residents, is a county located in the U.S. state of Indiana. As of the 2020 census, the population was 272,912, making it the fifth-most populous county in Indiana. Formed in 1830, it was named for the St. Joseph River which flows through it to Lake Michigan. The county seat is South Bend. St. Joseph County is part of the South Bend–Mishawaka, IN–MI "Michiana", Metropolitan Statistical Area.