Neighbouring municipalities are Kannonkoski, Kivijärvi, Kyyjärvi, Saarijärvi and Soini.

[5] The name of Karstula is likely derived from the Savonian surname Karstunen, encountered around Ristiina since 1541.

First records of the surname in Northern Tavastia (modern Central Finland) are from the 18th century.

Karstula was initially a part of the Saarijärvi parish, acquiring chapel rights in 1775 under it.

[6] Kannonkoski, Karstula, Kivijärvi and Kyyjärvi planned to merge into the Suomenselkä municipality [fi] from January 1, 2022.