Karksi-Nuia (before 1987 Nuia;[1] German: Karkus-Nuija) is a town in Mulgi Parish, Viljandi County, southern Estonia close to the Latvian border.

The nearest villages are Univere to the west, Polli and Karksi to the north, and Kõvaküla to the south.

When it was finally completed during the 14th century, it was for a time an important stronghold for the Teutonic Order in southern Estonia, and since 1470 the residence of the local commander.

[3][4] Karksi-Nuia is situated in the southern part of Viljandi County.

It is part of the Karksi Parish, a municipality that consists of the town and the 20 villages around it.