Importance: Although nearly 1 in 5 persons in the United States has a physical or mental disability, little is known about the association of the Patient Protection and Affordable Care Act (ACA) with health insurance coverage among persons with a disability. Objective: To determine the association of Medicaid expansion with health insurance coverage among persons with a disability. Design, Setting, and Participants: Cross-sectional analysis of adults eligible for Medicaid expansion (aged 26-64 years with incomes up to 138% of the federal poverty level), using a triple-differences (difference-in-difference-in-difference) approach to compare the pre-ACA with post-ACA trend in health insurance rates by disability status between expansion and nonexpansion states using nationally representative, repeated cross-sectional sample data obtained from the American Community Survey in the United States from January 1, 2010, to December 31, 2016. Time was defined as either pre-ACA (January 1, 2010, to December 31, 2013) or post-ACA (January 1, 2014, to December 31, 2016). Treatment status was defined as whether a state implemented Medicaid expansion after January 1, 2014. States that expanded Medicaid between January 1, 2014, to December 31, 2016, were classified as the treatment group, and states that did not expand Medicaid during the study period were classified as the control group. Data were analyzed from December 12, 2018, to May 21, 2019. Main Outcomes and Measures: Self-reported health insurance coverage (uninsured, Medicaid, private) and self-reported disability status (≥1 condition limiting activity, including cognitive, ambulatory, self-care, independent living, and sensory difficulties). Results: Of 2549376 Medicaid-eligible adults, 1 348 620 (52.9%) were female; 1 218 602 (47.8%) were non-Hispanic white, 497 128 (19.5%) were non-Hispanic black, 211 598 (8.3%) were Hispanic, and 206 499 (8.1%) were of other race/ethnicity; and 619 498 (24.3%) reported at least 1 disability. The percentage of persons without health insurance was greatest for persons without a disability who lived in a nonexpansion state before the ACA's Medicaid expansion provision went into effect (236 645 of 426 387 [55.5%]), and the smallest proportion of persons without health insurance was reported for persons with a disability living in an expansion state after the ACA went into effect (19 552 of 176 145 [11.1%]). Triple-differences analysis suggested that Medicaid expansion was associated with a decrease in the uninsured rate for both persons with a disability (7.1%-16.2% =-9.1%) and without a disability (21.2%-34.9% =-13.7%) and that Medicaid expansion was associated with a 4.6% decrease in the uninsurance rate for persons without a disability and a 2.6% decrease in persons with a disability (P <.001). Although Medicaid expansion was associated with an increase in Medicaid coverage for both persons with a disability (49.3% pre-ACA to 62.3% post-ACA; change, 13.0%) and persons without a disability (21.6% pre-ACA to 40.3% post-ACA; change, 17.7%), the triple difference-estimated Medicaid coverage was-4.7% for persons with a disability and 0.4% for persons without a disability, a difference of 5.1% (P <.001). Medicaid expansion was associated with a 3% higher private insurance rate for persons with a disability than for persons without a disability. Conclusions and Relevance: Medicaid expansion appeared to be associated with lower uninsurance rates and higher Medicaid and private insurance coverage for persons with a disability. This study's findings suggest that the reduction in the uninsured rate and gains in Medicaid coverage were greater for persons without a disability than for persons with a disability..