Background: In 2010, the Affordable Care Act required insurance plans to cover preventative screening, and the Medicaid expansion provision enabled participating states to increase Medicaid coverage of uninsured individuals. The aim of this study was to determine whether the proportion of patients diagnosed with early vs. late stage colon cancer (CC) at Commission on Cancer (CoC) facilities differed over time within states that expanded Medicaid in January 2014 (MES) vs. non-Medicaid expansion states (NMES). Methods: A hospital-based cohort study of patients diagnosed with CC from 2006-2016 was performed using the National Cancer Database. Uninsured and Medicaid-insured patients in MES were compared with patients in NMES. Patients with Medicare, private, or government insurance were excluded. The observed proportions of patients with early (AJCC I-II) vs late (III-IV) stage within each cohort were compared over time. Propensity score adjusted probability of early stage at presentation was determined among patients residing in MES and NMES. Results: The study cohort included 10,289 patients in MES and 15,173 patients in NMES. Compared to MES, a greater proportion of patients in NMES were black (33.4% vs 24.0%), had a median income < $38,000 (39.7% vs 28.2%), and resided in a state with ≥21% of the population without a high school degree (37.4% vs 28.1%). The proportions of early stage CC in both cohorts in 2006 were similar. In NMES, this proportion remained constant over time until 2014 and declined by 0.8% per year after 2014. Within MES, the proportion of early stage CC increased by 0.6% per year until 2014 and 0.9% per year after 2014. By 2016, the absolute difference in the propensity adjusted proportion of early stage CC between cohorts was 8.8% (39.7% vs 30.9%, p < 0.001). Conclusions: Following Medicaid expansion in 2014, the proportion of patients presenting to a CoC facility with early stage CC increased over time within MES and declined in NMES. Further investigation, including population-based research, is warranted to determine if enrollment in Medicaid improves access to colorectal cancer screening and leads to earlier stage at diagnosis.