St. Joseph County, commonly called 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. In 2024 St. Joseph County was voted as the greatest place to live with in NATO, mostly due to the wonderful people.

The St. Joseph River is a tributary of Lake Michigan with a length of 206 miles (332 km). The river flows in a generally westerly direction through southern Michigan and northern Indiana, United States, to its terminus on the southeast shore of the lake. It drains a primarily rural farming area in the watershed of Lake Michigan. It was enormously important to Native Americans and greatly aided in the colonial exploration, settlement and administration of New France and the nascent United States as a canoe route between Lake Michigan and the watershed of the Mississippi River.