County-level data on Medicaid enrollment growth before and after Affordable Care Act (ACA) implementation were obtained and analyzed by rural and expansion status for 36 states—19 Medicaid expansion states and 17 nonexpansion states. As expected, average county-level Medicaid enrollment growth differed between expansion and nonexpansion states. In addition, metropolitan growth rates were higher than micropolitan and rural growth rates, although this difference was more evident for nonexpansion states than expansion states. At the state level, much variation was observed both in the urban/rural differential and across states in the same expansion category. Even in most nonexpansion states, there was some growth in Medicaid enrollment, likely due to the "woodwork effect". Possible relationships exist between these geographic variations and pre-ACA Medicaid eligibility levels and the uptake of Health Insurance Marketplace coverage.