PURPOSE Given the increasing incidence of early-onset colorectal cancer (CRC; diagnosed before age 50 years) worldwide, it is important to identify modifiable risk factors. We investigated whether alcohol consumption in the young population correlated with an increased early-onset CRC risk that differed by tumor location and sex. PATIENTS AND METHODS We investigated the association between average daily alcohol consumption and the risk of early-onset CRC among 5,666,576 individuals age 20-49 years using data from the Korean National Health Insurance Service (2009-2019). Alcohol consumption levels of nondrinker, light (reference), moderate, and heavy drinker were defined as 0, <10, 10 to <30, and ≥30 g/d for men and 0, <10, 10 to <20, and ≥20 g/d for women, respectively. Multivariate Cox proportional hazards models were used to estimate adjusted hazard ratios (aHRs) with 95% CIs. RESULTS We identified 8,314 incident early-onset CRC cases during the follow-up period. Moderate and heavy drinkers showed an increased risk of early-onset CRC compared with light drinkers (aHR, 1.09; 95% CI, 1.02 to 1.16 and aHR, 1.20; 95% CI, 1.11 to 1.29, respectively). Subgroup analysis by tumor location showed positive dose-response significance for early-onset distal colon and rectal cancers, but not for proximal colon cancer. The dose-response association between drinking frequency and risk of early-onset CRC was significant, with a 7%, 14%, and 27% increased risk for 1-2, 3-4, and ≥5 d/wk compared with nondrinkers, respectively. CONCLUSION Excessive alcohol consumption increases the risk of CRC onset before age 50 years. Thus, effective interventions are required to discourage alcohol consumption among young people and to tailor CRC screening approaches for high-risk individuals.