Cimarron is an unincorporated community and U.S. Post Office in Montrose County, Colorado, United States. The Cimarron Post Office has the ZIP Code 81220.Cimarron is a small unincorporated community on the Cimarron River, just south of the Black Canyon of the Gunnison, and just outside of Curecanti National Recreation Area. The D & RG Narrow Gauge Trestle crosses the Cimarron River gorge just northeast of town, and is on the National Register of Historic Places (#76000172).