This study compared mental health treatment engagement among people with serious mental illness after release from jails that had either a for-profit (N=3 jails) or a nonprofit mental health provider (N=7 jails). Across the 10 jails, data were collected in 2019 for 1,238 individuals with serious mental illness. Data included demographic characteristics (age, race-ethnicity, gender, geography, and jail type) and behavioral health variables (previous mental health treatment, psychotropic medication use, substance use, and receipt of jail-based mental health services). Logistic regression was used to predict treatment engagement during the year after release, stratified by type of jail-based mental health provider, in analyses controlled for demographic and behavioral health variables. Almost half (46%, N=573) of the individuals had stayed in jails with a for-profit mental health provider; the other half (54%, N=665) had stayed in jails with a nonprofit provider. In the year after release, 37% (N=458) of all individuals engaged in mental health treatment, and 63% (N=780) did not. Those who had stayed in a jail with a for-profit provider were significantly less likely to engage in mental health treatment during the year after release (AOR=0.59, 95% CI=0.42-0.83, p<0.01), compared with those in jails having a nonprofit provider. Staying in a jail with a for-profit mental health provider was associated with reduced postrelease engagement with community service providers. Less engagement with services during a pivotal time after release may increase behavioral health crises that erode individuals' well-being and may raise downstream costs due to further criminal legal involvement and emergency care use.