Rio Arriba County, N.M.

With the occupation of New Mexico in 1846 by the United States, seven political subdivisions established by Mexico in 1844 were recognized as counties under the Kearny Code of Laws. Rio Arriba County was one of these seven original counties. New Mexico remained under a military form of government until Sept. 9, 1850, when an act of Congress established the Territory of New Mexico. On Jan. 9, 1852, the boundaries of the counties were fixed by an act of the Territorial Legislative Assembly. Rio Arriba County, New Mexico was created in 1852.