Background: Early mortality after resection of locally advanced rectal cancer in patients age 75 and older has not been studied in the United States. This information could inform clinical decision-making for patients who achieve complete clinical response after neoadjuvant therapy and consider watchful waiting versus surgical resection. Methods: Using the National Cancer Data Base, we identified patients age 75 years and older who underwent surgery for clinical stage II or III rectal cancer between 2004-2015. We performed multivariable logistic regression analyses to assess associations between patient and facility characteristics and 30-day, 90-day, and 6-month mortality. Results: Among 11,326 patients, 94% underwent resection and the remaining 6% underwent local excision. Overall early mortality rates after surgery were 4%, 7.6% and 11% for 30-day, 90-day and six-month, respectably. Six-month mortality varied by age subgroup (8% in 75-79 years old to 17.7% in 85 years and older), and comorbidity score (9.5% for comorbidity score = 0 to 18.5% for comorbidity score ≥ 2). Between 2004 and 2015, six-month mortality declined significantly from 11.9% in 2004-2007 to 9.8% in 2012-2015 (P trend = 0.0029), with the decline larger among patients age 85 years and older (from 19.4% in 2004-2007 to 15.3% in 2012-2015, P trend = 0.0377). In the multivariable analysis, older age, higher comorbidity score, and lower facility case volume were significantly associated with higher odds of six-month mortality. Patients treated at National Cancer Institute (NCI) designated centers had 32% lower odds of six-month mortality compared with those treated at non-NCI designated teaching/research centers. Conclusions: Post-operative six-month mortality among patients age 75 years and older with locally advanced rectal cancer in the US declined steadily over the past decade. Older age, high comorbidity score, and low facility case volume were associated with higher six-month mortality after surgery. Additional efforts are needed to guide elderly patients and their physicians in discussing treatment options for locally advanced rectal cancer.