PURPOSE: Our objective was to describe differences in treatment patterns and survival between early-onset (< 50 years old) and late-onset colorectal cancer (CRC) patients in community-based health systems. METHODS: We used tumor registry and electronic health record data to identify and characterize patients diagnosed with adenocarcinoma of the colon or rectum from 2010 to 2014 at six US health systems in the patient outcomes to advance learning (PORTAL) network. We used logistic regression to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) comparing the distribution of tumor characteristics and treatment patterns in early-onset versus late-onset CRC. Cox regression models were used to estimate adjusted hazard ratios (HRs) and CIs comparing survival between early- and late-onset CRC patients. RESULTS: There were 1,424 early-onset and 10,810 late-onset CRC cases in our analyses. Compared to late-onset CRC, early-onset CRC was significantly associated with advanced-stage disease, high-grade histology, signet ring histology, and rectal or left colon location. After adjusting for differences in tumor and patient characteristics, early-onset patients were more likely than late-onset patients to have > 12 lymph nodes examined (OR 1.60, CI 1.37-1.87), to receive systemic therapy (chemotherapy or immunotherapy) within 6 months of diagnosis (OR 2.84, CI 2.40-3.37), and to have a reduced risk of CRC-specific death (HR 0.66, CI 0.56-0.79). CONCLUSIONS: Early-onset CRC is associated with aggressive tumor characteristics, distal location, and systemic therapy use. Despite some adverse risk factors, these patients tend to have better survival than older onset patients.