To investigate depression at 12 months after traumatic brain injury (TBI) in older adults compared with younger adults. Prospective longitudinal cohort study of persons with medically documented mild, moderate, and severe TBI at 12 months postinjury. Eighteen participating Level 1 trauma centers in the United States. Participants with TBI (N=1505) and primary outcome data at 12-month follow-up. Not applicable. Patient Health Questionnaire-9 (PHQ-9). PHQ-9 total scores were significantly lower for older adults (age≥65y; M=3.2) compared with younger adults (age<65y; M=5.0; B=-1.63, P<.001), indicating fewer depressive symptoms in older adults. Age did not interact with education, sex, race/ethnicity, psychiatric history, substance use, or Glasgow Coma Scale severity to affect PHQ-9 scores. Of the 29% of older adults who endorsed symptoms consistent with depression, 14% were classified as minor depression and 15% as major depression. The odds of older adults falling in the major depression vs no depression group were significantly lower (decreased by 56%) compared with younger adults (odds ratio=0.44, P=.001). At 12 months post-TBI, older adults endorse lower depressive symptoms than their younger counterparts and are less likely to experience major depression; however, over one-fourth of older adults endorsed symptoms consistent with depression, warranting evaluation and treatment.