Jaroso is an unincorporated community and a U.S. Post Office located in Costilla County, Colorado, United States. The Jaroso Post Office has the ZIP Code 81138.A post office called Joroso has been in operation since 1911. Jaroso is a name derived from Spanish meaning "willows".Jaroso is located at 37°00′14″N 105°37′26″W / 37.00389°N 105.62389°W / 37.00389; -105.62389.