The Supreme Court ruling on the Affordable Care Act upheld the individual mandate and made the expansion of Medicaid coverage to nonelderly adults with incomes below 138 percent of the federal poverty level optional for states. In this brief, Urban Institute researchers estimate the number of uninsured Americans in each state who could be eligible for Medicaid if every state takes the option of expanding Medicaid coverage. Of 22.3 million uninsured Americans who could be potentially eligible for Medicaid under the ACA, 67 percent (15.1 million) are adults not currently eligible for Medicaid. Of this group, 11.5 million have incomes below poverty and would not qualify for any other subsidized coverage.