Medicaid expansion has been shown to improve access to care, health, and finances in general populations. Until now no studies have considered how Medicaid expansion may affect informal family caregivers who are the backbone of the long term supports and services infrastructure. Family caregivers provide substantial cost savings to Medicare and Medicaid. Yet, they sustain financial, physical, and mental health strain from their caregiving role which Medicaid expansion may offset. This study evaluated the impact of Medicaid expansion on caregivers' mental health using 2015–2018 data from the Behavioral Risk Factor Surveillance System. After adjusting for demographics, socioeconomic status, and health behaviors, caregivers in Medicaid expansion states had a significantly fewer number of poor mental health days in the previous month than caregivers in non-expansion states (ß = −0.528, CI −1.019, −0.036, p <.01). Study findings indicate that Medicaid expansion state status was protective for caregiver's mental health.