Individuals with co-occurring illnesses are at risk for poor outcomes related to criminal justice, hospitalization, housing, and employment. High fidelity evidence-based models, including integrated dual disorder treatment (IDDT), are associated with significant outcome improvements. A descriptive analysis of secondary datasets including the full sample of IDDT fidelity reviews completed from 2006 to 2012 in one state was completed. Total IDDT fidelity significantly improved from baseline fidelity review (68) to second review (40) [t(38) = 35.00, p < .001], and from second review to third review (13) [t(12) = 22.60, p < .001], with adequate inner-rater reliability by the second review. Individual items that were lower across reviews included practice penetration and family interventions, and higher individual items included multi-disciplinary team, integrated treatment specialist, and time-unlimited services, and treatment measures are higher than organizational measures in baseline and subsequent reviews. In this large state-wide sample, IDDT took time to implement, and improved fidelity occurred from baseline to third review, and variance between components of the practice was significant.