Rio Arriba County is a county located in the U.S. state of New Mexico. As of the 2010 census, the population was 40,246. Its county seat is Tierra Amarilla. Its northern border is the Colorado state line. Three major lakes, National Forest and State Parks attrinute to the many outdoor activities that abound. Several activities include fishing, boating, camping, water skiing, sailing, hiking, winter sports, camping, and picnicking. With the skyrocketing land pricesand activities in Arizona and Colorado, Northern New Mexico is experiencing a surge in activities and real estate purchaes.