Rio Arriba County is located in north central New Mexico.

Most of the county is made up of old Spanish and Mexican Land Grants, although a lot of the land is also part of Carson National Forest. Many of the families in the area became established here as early as the 1500's. Rio Arriba County is a center of activity for Los Hermanos Pentitentes with moradas scattered throughout the countryside.

Several Pueblo Reservations and the Jicarilla Apache Reservation are in Rio Arriba County, too.

Formed in 1852, Rio Arriba County contains 5,858 square miles of land and 38 square miles of water.

The county seat is Tierra Amarilla.