Context: Knee osteoarthritis (OA) frequently develops following knee injury/surgery. It is accepted that knee injury/surgery precipitates OA with previous studies examining this link in terms of years after injury/surgery. However, postinjury OA prevalence has not been examined by decade of life; thereby, limiting our understanding of the age at which patients are diagnosed with posttraumatic knee OA. Objective: Evaluate the association between the knee injury and/or surgical history, present age, and history of receiving a diagnosis of knee OA. Design: Cross-sectional survey. Setting: Online survey. Participants: A total of 3660 adults were recruited through ResearchMatch©. Of these, 1723 (47.1%) were included for analysis due to history of (1) knee surgery (SURG: n = 276; age = 53.8 [15.3] y; and body mass index [BMI] = 29.9 [8.0] kg/m2), (2) nonsurgical knee injury (INJ: n = 449; age = 46.0 [15.6] y; and BMI = 27.5 [6.9] kg/m2), or (3) no knee injury (CTRL: n = 998; age = 44.0 [25.2] y; and BMI = 26.9 [6.6] kg/m2). Respondents were subdivided by decade of life (20–29 through 70+). Intervention: An electronic survey regarding knee injury history, treatment, and diagnosis of knee OA. Main Outcome Measures: Binary logistic regression determined the association between knee surgical status and OA by decade of life. Participants with no histories of OA or lower-extremity injury were the referent categories. BMI was a covariate in all analyses. Results: SURG respondents were more likely to report having knee OA than CTRL for all age groups (odds ratios: 11.43–53.03; P < .001). INJ respondents aged 30 years and older were more likely to have OA than CTRL (odds ratios: 2.99–14.22; P < .04). BMI influenced associations for respondents in their 50s (P = .001) and 60s (P < .001) only. Conclusions: INJ increased the odds of reporting a physician diagnosis of knee OA in adults as young as 30 to 39 years. Importantly, SURG yielded 3 to 4 times greater odds of being diagnosed with knee OA compared with INJ in adults as young as 20 to 29 years. Delaying disease onset in these young adults is imperative to optimize the quality of life long term after surgery.