To explore risks and associated mediation effects of developing chronic kidney disease (CKD) and heart failure (HF) in young- and usual-onset type 2 diabetes (T2D) between White Americans (WAs) and African Americans (AAs).From U.S. medical records, 1,491,672 WAs and 31,133 AAs were identified and stratified by T2D age of onset (18-39, 40-49, 50-59, 60-70 years). Risks, mediation effects, and time to CKD and HF were evaluated, adjusting for time-varying confounders.In the 18-39, 40-49, 50-59, 60-70 age-groups, the hazard ratios (of developing CKD and HF in AAs versus WAs were 1.21 (95% CI 1.17-1.26) and 2.21 (1.98-2.45), 1.25 (1.22-1.28) and 1.86 (1.75-1.97), 1.21 (1.19-1.24) and 1.54 (1.48-1.60), and 1.10 (1.08-1.12) and 1.11 (1.07-1.15), respectively. In AAs and WAs aged 18-39 years, time in years to CKD (8.7 [95% CI 8.2-9.1] and 9.7 [9.2-10.2]) and HF (10.3 [9.3-11.2] and 12.1 [10.6-13.5]) were, on average, 3.6 and 4.0 and 3.1 and 4.1 years longer compared with those diagnosed at age 60-70 years. Compared with females, AA males aged <60 years had an 11-49% higher CKD risk, while WA males aged <40 years had a 23% higher and those aged ≥50 years a 7-14% lower CKD risk, respectively. The mediation effects of CKD on the HF risk difference between ethnicities across age-groups (range 54-91%) were higher compared with those of HF on CKD risk difference between ethnicities across age-groups (13-39%).Developing cardiorenal complications within an average of 10 years of young-onset T2DM and high mediation effects of CKD on HF call for revisiting guidelines on early diagnosis and proactive treatment strategies for effective management of cardiometabolic risk.