| | Archuleta County | CO | 08007 | | | | | nonmetro county (rural) | recreation | https://maps.google.com/?q=ArchuletaCounty+CO |
| | Arapahoe County | CO | 08005 | | Denver-Aurora-Centennial,
CO 19740 | Denver-Aurora-Greeley, CO 216 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=ArapahoeCounty+CO |
| | Alamosa County | CO | 08003 | | Alamosa, CO 10480 | | Central | nonmetro county (rural) | federal/state
government-dependent | https://maps.google.com/?q=AlamosaCounty+CO |
| | Adams County | CO | 08001 | | Denver-Aurora-Centennial,
CO 19740 | Denver-Aurora-Greeley, CO 216 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=AdamsCounty+CO |