Treatment completion is an important outcome for both mental health and criminal justice agencies tasked with managing offenders with mental illness in the community. Previous research has shown that greater degrees of criminogenic risk factors (e.g., specific criminal history variables) predict treatment non-completion among legally mandated populations. However, most studies were conducted with offenders without mental illness. In this study, demographic (e.g., age, gender), clinical (e.g., psychiatric diagnosis), and criminogenic risk factors (measured using the Level of Service Inventory–Revised [LSI-R]) were compared by treatment completion status using 167 probationers with mental illness treated at an enhanced day reporting center. Bivariate and multivariate (i.e., forward entry logistic regression) analyses revealed that while the LSI-R total score was unrelated to treatment completion, higher scores on the LSI-R Alcohol and Drug use subscale (odds ratio [OR] = 1.25, 95% confidence interval [CI] = [1.01, 1.54]) and older age (OR = 1.04, 95% CI = [1.00, 1.09]) were significantly predictive of non-completion.