Matanuska-Susitna Borough is a borough located in the U.S. state of Alaska. Its borough seat is Palmer, and the largest community is the census-designated place of Knik-Fairview. As of the 2020 census, the borough's population was 107,801. The borough is part of the Anchorage Metropolitan Statistical Area, along with the municipality of Anchorage on its south. The Mat-Su Borough is so designated because it contains the entire Matanuska and Susitna Rivers.