Complex sentence: St. Joseph (informally St. Joe) is the county seat of Buchanan County and chief city of the St. Joseph Metropolitan Statistical Area, which includes Buchanan, Andrew, and DeKalb counties in Missouri and Doniphan County, Kansas.
Split into simpler sentences: St. Joseph (informally St. Joe) is a city in and the county seat of Buchanan County, Missouri, United States. 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.