Purpose. From October 2013—before implementation of the Affordable Care Act (ACA)—to November 2016, Medicaid enrollment grew by 27 percent. However, very little attention has been paid to date to how changes in Medicaid enrollment vary within states across the rural-urban continuum. This brief reports and analyzes changes in enrollment in metropolitan, micropolitan, and rural (noncore) areas in both expansion states (those that used ACA funding to expand Medicaid coverage) and nonexpansion states (those that did not use ACA funding to expand Medicaid coverage). The findings suggest that growth has been uneven across rural-urban geography, and that Medicaid enrollment growth is lower in rural counties, particularly in nonexpansion states. Key Findings. (1) Medicaid growth rates in metropolitan counties in nonexpansion states from 2012 to 2015 were twice as large as in rural counties (14 percent compared to 7 percent). (2) In contrast, the differential in growth rates between metropolitan, micropolitan, and rural counties was much less dramatic in expansion states (growth rates of 43 percent, 38 percent, and 38 percent, respectively). (3) Analysis at the state level shows much variability across the states, even when controlling for expansion status. For example, some states with an above-average rural population, such as Tennessee and Idaho, had higher-than-average enrollment increases, with strong rural increases, while other states with similar proportions of rural residents, such as Nebraska, Oklahoma, Maine, and Wyoming, experienced enrollment decreases in micropolitan and/or rural counties. (4) States’ pre-ACA Medicaid eligibility levels for parents and children affected the potential for growth. For example, some states that had higher eligibility levels (e.g., Maryland and Illinois) experienced lower Medicaid growth rates from 2012 to 2015, in part because their baseline enrollment was higher. (5) In the expansion states of Colorado and Nevada, which both have State-Based Marketplaces (SBMs), enrollment increases were over four times the overall average.