Calhoun County is a county in the U.S. state of Michigan. As of the 2020 Census, the population was 134,310. The county seat is Marshall. The county was established on October 19, 1829, and named after John C. Calhoun, who was at the time Vice President under Andrew Jackson, making it one of Michigan's Cabinet counties. County government was first organized on March 6, 1833.