The incidence and longitudinal trends of patients with ST-elevation myocardial infarction (STEMI) presenting to United States (US) emergency departments (EDs) are currently unknown. Efforts to use effective treatments for cardiovascular disease may decrease ED STEMI presentation. We conducted a descriptive epidemiological analysis of STEMI visits to EDs from 2006 to 2011 using the Nationwide ED Sample, the largest source of US ED data, to determine the incidence of patients with STEMIs presenting to the US EDs. We included adult ED visits with an International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis of STEMI and calculated incidence rates for STEMI ED visits using US census population data. Incidence calculations were stratified by age group, geographic region, and year. From 2006 to 2011, there was a mean of 258,106 STEMIs presenting to EDs per year, decreasing from 300,466 in 2006 to 227,343 in 2011. Incidence of ED STEMI visits per 10,000 adults decreased from 10.1 (95% confidence interval [CI] 9.8 to 10.8) in 2006 to 7.3 (95% CI 6.8 to 7.8) in 2011. The Midwest had the highest rate of ED STEMIs at 10.0 (95% CI 9.2 to 10.8) and the West had the lowest with 6.6 (95% CI 6.1 to 7.0). The incidence of STEMI decreased for all age groups during the study period. In conclusion, we report the first national estimates of STEMI presentation to US EDs, which demonstrate decreasing incidence across all age groups and all geographic regions from 2006 to 2011. A decreasing STEMI incidence may affect the quality and timeliness of STEMI care. Continued national STEMI surveillance is needed to guide healthcare resource allocation.