We sought to develop a county-level measure to evaluate residents' access to exercise opportunities. Data were acquired from Esri, DeLorme World Vector (MapMart), and OneSource Global Business Browser (Avention). Using ArcGIS (Esri), we considered census blocks to have access to exercise opportunities if the census block fell within a buffer area around at least 1 park or recreational facility. The percentage of county residents with access to exercise opportunities was reported. Measure validity was examined through correlations with other County Health Rankings & Roadmaps' measures. Included were 3,114 of 3,141 US counties. The average population with access to exercise opportunities was 52% (range, 0%-100%) with large regional variation. Access to exercise opportunities was most notably associated with no leisure-time physical activity (r = -0.47), premature death (r = -0.38), and obesity (r = -0.36). The measure uses multiple sources to create a valid county-level measure of exercise access. We highlight geographic disparities in access to exercise opportunities and call for improved data.