
Matanuska-Susitna Borough (often referred to as the Mat-Su 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. They empty into Cook Inlet, which is the southern border of the Mat-Su Borough. It is one of the few agricultural areas of Alaska.