Appalachian Kentucky (AK) has a disproportionally high breast cancer mortality rate. Postmastectomy radiotherapy (PMRT) in N2/N3 nodal disease improves survival and locoregional recurrence. We evaluated Kentucky patient compliance to the quality measure of PMRT received within one year of diagnosis. A population-based retrospective review of patients who received mastectomy with N2/N3 nodal disease from 2006 to 2015 was obtained through the Kentucky Cancer Registry. A total of 1489 patients met the inclusion criteria. Of these, 1104 (66.6%) received PMRT. AK patients were less likely to receive PMRT (58.3%) than non-AK patients (70%, < 0.001). After adjusting for significant factors, private insurance, education level, treatment center, and receipt of adjuvant chemotherapy were independently associated with PMRT compliance. Patients who received PMRT had improved overall survival (OS, < 0.0001) and disease-free survival (DFS, < 0.0001). Appalachian status was not a major factor in OS (= 0.1929) or DFS ( = 0.5840). Nearly two decades after the recommendation of PMRT, compliance remains poor in Kentucky. PMRT continues to be a major factor in survival and recurrence in this population. Interventions focusing on improving insurance coverage, education level, and guideline adherence in nonacademic centers are needed to improve compliance.