Owosso is the largest city in Shiawassee County in the U.S. state of Michigan. The population was 14,714 at the 2020 census. It is locateā¦Owosso is the largest city in Shiawassee County in the U.S. state of Michigan. The population was 14,714 at the 2020 census. It is located 29 miles west of Flint, and 32 miles northeast of Lansing. The city is mostly surrounded by Owosso Township on its west, but the two are administered autonomously. The city was named after Chief Wosso, an Ojibwe leader of the Shiawassee area.