Recent research has shown that concern about the apprehension and deportation of undocumented immigrants can affect how members of their households who are eligible for public benefits choose to participate in public programs. The extent to which this “chilling effect” broadly affects adults’ Medicaid enrollment nationally remains unclear, in part because of the difficulty of isolating undocumented immigrants in survey data. In this study we identified households that likely included undocumented immigrants and then examined whether gains in health care coverage due to the expansion of Medicaid eligibility under the Affordable Care Act (ACA) were dampened for eligible people living in households with mixed immigration status. We found no significant differences in coverage gains for people in mixed- relative to non-mixed-status households in expansion states. Coverage gains were significantly lower, however, for people in mixed-status households relative to those in non-mixed-status households in nonexpansion states. These findings suggest that household immigration status may have dampened the “woodwork effect,” whereby the ACA enhanced knowledge about program availability, in turn increasing Medicaid enrollment in nonexpansion states among people previously eligible for the program but not enrolled in it.