Matanuska-Susitna Borough (often referred to as the Mat-Su Borough) is a borough located in the U.S. state of Alaska.
The borough seat is Palmer, and the largest city is Wasilla.
As of the 2010 census, the population was 88,995.
According to the U.S. Census Bureau, the borough has a total area of 25,258 square miles (65,420 km), of which 24,608 square miles (63,730 km) is land and 650 square miles (1,700 km) (2.6%) is water.
As of the census of 2000, there were 59,322 people, 20,556 households, and 15,046 families residing in the borough. The population density was 2 people per square mile (1/km²). There were 27,329 housing units at an average density of 1 per square mile (0/km²). The racial makeup of the borough was 87.55% White, 0.69% Black or African American, 5.50% Native American, 0.70% Asian, 0.12% Pacific Islander, 0.86% from other races, and 4.57% from two or more races. 2.50% of the population were Hispanic or Latino of any race.
There were 20,556 households out of which 42.30% had children under the age of 18 living with them, 58.90% were married couples living together, 9.10% had a female householder with no husband present, and 26.80% were non-families. 20.30% of all households were made up of individuals and 4.10% had someone living alone who was 65 years of age or older. The average household size was 2.84 and the average family size was 3.29.
In the borough the population was spread out with 32.20% under the age of 18, 7.40% from 18 to 24, 31.10% from 25 to 44, 23.40% from 45 to 64, and 5.90% who were 65 years of age or older. The median age was 34 years. For every 100 females, there were 108.20 males. For every 100 females age 18 and over, there were 108.10 males.
Schools in the borough are administered by the Matanuska-Susitna Borough School District.