The Székelys of Harghita are mostly Roman Catholic, with Reformed and Unitarian minorities, while the ethnic Romanians are primarily Orthodox.

Catholicism is strongest in the east, in the former Csíkszék, while Protestants are concentrated in the south and west of Odorheiu Secuiesc.

Harghita consists primarily of mountains, connected to the Eastern Carpathians, such as the Ciuc and Harghita Mountains; volcanic plateaux, foothills, and the more densely populated river valleys.

The mountains are volcanic in origin, and the region is known for its excellent hot mineral springs.

Harghita's spectacular natural scenery includes Sfânta Ana Lake, a volcanic crater lake near the town of Băile Tușnad; Lacul Roșu a mountain lake in the northeast near the town of Gheorgheni, and Cheile Bicazului, a dramatic, narrow canyon formed by the Bicaz stream.