The Affordable Care Act expands Medicaid in 2014 to millions of low-income adults in states that choose to participate in the expansion. Since 2010 California, Connecticut, Minnesota, and Washington, D.C., have taken advantage of the law’s option to expand coverage earlier to a portion of low-income childless adults. We present new data on these expansions. Using administrative records, we documented that the ramp-up of enrollment was gradual and linear over time in California, Connecticut, and D.C. Enrollment continued to increase steadily for nearly three years in the two states with the earliest expansions. Using survey data on the two earliest expansions, we found strong evidence of increased Medicaid coverage in Connecticut (4.9 percentage points; (p<0.001)) and positive but weaker evidence of increased coverage in D.C. (3.7 percentage points; (p=0.08)). Medicaid enrollment rates were highest among people with health-related limitations. We found evidence of some crowd-out of private coverage in Connecticut (30–40 percent of the increase in Medicaid coverage), particularly for healthier and younger adults, and a positive spillover effect on Medicaid enrollment among previously eligible parents.
