St. Joseph (informally St. Joe) is a city in and the county seat of Buchanan County, Missouri, United States. Small parts of St. Joseph extend into Andrew County, Missouri. It is the principal city of the St. Joseph Metropolitan Statistical Area, which includes Buchanan, Andrew, and DeKalb counties in Missouri and Doniphan County, Kansas. As of the 2010 census, St. Joseph had a total population of 76,780, making it the eighth largest city in the state, and the third largest in Northwest Missouri. St.