Purpose <p>The 2010 Affordable Care Act (ACA) expanded access to depression screening and care. However, changes in unmet need for depression treatment and public mental health equity following ACA implementation remain understudied.</p> Methods <p>Data from 3,522 respondents to the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2020 were used to examine changes in clinically significant depression symptoms that received neither with pharmacologic nor behavioral health treatment. Modified Poisson regression models were used to estimate the association between time period (post-ACA, 2013–2020 vs. pre-ACA, 2005–2010) and unmet need for depression treatment, both overall and stratified by socio-demographic and health care-related variables.</p> Results <p>Unmet need for depression treatment decreased from 56% in 2005-10 to 47% in 2013-20, with no significant differences by socio-demographic characteristics. After adjusting for covariates, this corresponded to a 14% reduction in unmet need post- vs. pre-ACA (prevalence ratio (PR) 0.86; CI 0.79,0.95). Only those reporting Medicare vs. another type of insurance coverage experienced a significant decrease in unmet need for depression treatment (PR 0.77; CI 0.60,0.99). A similar decrease in unmet need was observed regardless of having a regular point of care or not, but only detected among those who had used health care services in the prior year (PR 0.80; CI 0.70,0.92) vs. those who had not (PR 1.13; CI 0.92,1.37).</p> Conclusion <p>Unmet need for depression treatment decreased after ACA implementation but remains common. Reductions in barriers to primary care visits and universal screening policies may further decrease unmet need for depression treatment.</p>