Objective To assess the impact of Enroll America's field outreach activities on the number of individuals enrolled in Marketplace coverage during the first open enrollment period. Data Sources/Study Setting Marketplace enrollment for the initial open enrollment period linked with data on Enroll America's field activities and baseline local‐area demographic, economic, and health services characteristics. Study Design We used a quasi‐experimental design, comparing Marketplace enrollment during the first open enrollment period in local areas drawn from Enroll America field states to a comparison group of local areas drawn from states that were not served by Enroll America's field effort, but that otherwise match up well with Enroll America states. Principal Findings We find evidence of a large, positive effect of Enroll America's field outreach on Marketplace enrollment in non‐Medicaid expansion states. Across model specifications, the Enroll America effects on Marketplace enrollment ranged between 10 and 15 percent, with most estimates statistically significant at the 5 percent level. Conclusions Enroll America played an important role in the success of individual states' efforts to boost Marketplace enrollment. Enroll American's evidence‐driven, grassroots approach could serve as a model for others interested in conducting similar outreach campaigns for Affordable Care Act–related coverage.