Mullsjö Municipality is a municipality in Jönköping County, southern Sweden. Its seat is in the locality of Mullsjö.

Jönköping County is a county or län in southern Sweden. It borders the counties of Halland, Västra Götaland, Östergötland, Kalmar and Kronoberg. The total county population was 356,291 inhabitants in September 2017. The capital and largest city is Jönköping. About one quarter of the total county population lives in the combined Jönköping-Huskvarna urban area around the southern point of Lake Vättern.