Purpose We sought to examine the demographic, market, and policy‐related factors influencing first year enrollment rates for the population targeted by the Health Insurance Marketplaces (HIMs) established as part of the Affordable Care Act. In particular, we analyzed differences in enrollment rates across urban and rural counties in 32 states served by the Federally Facilitated Marketplace. Methods We used enrollment data from the Assistant Secretary for Planning and Evaluation of the US Department of Health and Human Services and demographic data from the American Community Survey, supplemented with other market and policy‐related information. Using multivariate regression, we investigated how county‐level enrollment rates are associated with demographic, market and policy‐related characteristics, including rurality. Findings Relative to an adjusted mean enrollment rate of 17.1% for large metropolitan counties, small metropolitan counties have a 2.8% lower enrollment rate and rural counties have a 2.7% lower enrollment rate. States’ decisions to expand Medicaid and to have the federal government fully manage the HIM are both negatively associated with enrollment rates. Partnership HIMs exhibit a positive association with enrollment rates as do navigator grants, but the latter relationship is only present in counties located in Medicaid expansion states. Conclusions Enrollment rates vary by rurality, but differences are statistically significant only between large metropolitan counties and all other types of counties—small metropolitan, micropolitan, and noncore. State‐level policies, particularly Medicaid expansion, have the largest association with enrollment rates among the explanatory variables examined in the model.