Leonessa is a town and comune in the far northeastern part of the Province of Rieti in the Lazio region of central Italy.

Terminillo, one of the highest mountains of the Apennine range, in the winter Leonessa is known mostly as a low-key staging center for the ski slopes of the Terminillo, and in the summer as a weekend vacation town frequented for the most part by Romans with local roots.

The town suffered one of the worst German reprisals during World War II when the Wehrmacht and the SS killed 51 inhabitants in early April 1944.

Typical food production include the local variety of potato, known as patata di Leonessa.

Leonessa is an art city of primarily medieval aspect, with a historical main square.