Background: It is well accepted that positive serum carcinoembryonic antigen (CEA) levels are associated with inferior survival in patients with advanced non-metastatic colon cancer; however, it is not fully elucidated whether this prognostic factor can inform clinical decisions, specifically for the optimal timing of adjuvant chemotherapy after definitive surgical treatment. This study was aimed to determine the relationship between onset of adjuvant chemotherapy and rate of survival in stage III colon cancer patients who tested CEA-positive, and thus, potentially identifying the optimal timing to increase survivorship. Methods: We identified 19,180 patients from the NCDB with TNM pathologic stage IIIB and IIIC adenocarcinoma of the colon who also had a recorded CEA test result and whom had received adjuvant chemotherapy. We examined unadjusted overall survival based on CEA status with the Kaplan-Meier method. A multivariable Cox regression model was estimated to determine the association of CEA status and overall survival after controlling for site, stage, days from surgery to chemotherapy, demographic background, and facility characteristics. All analyses were conducted with SAS version 9.4 (SAS Institute Inc., Cary, NC) with a statistical threshold of p < 0.05. Results: Based on the log-rank χ² test, a positive CEA test result was significantly associated with worse survival. We adjusted for patient and facility level characteristics, and found a 49.7% increased risk of death for a patient with a positive CEA result (95% CI: 41.7% to 58.2%). We found a median number of 43 days from definitive surgery to initiation of chemotherapy; after adjusting for all other variables, we found for every ten-day delay in receiving adjuvant therapy after definitive surgical intervention, there was a 1.6% increased risk of death (95% CI: 1.0 to 2.2%). Conclusions: In this cohort of patients who tested CEA-positive, delays in receiving adjuvant chemotherapy had a negative linear association on survival. Adjuvant therapy should be considered as soon as patient’s clinical condition permits.