Background: Young-onset colorectal cancer (yCRC) diagnosed under age 50 is increasing at alarming rates, with >75% of young-onset cases occurring in patients between 40-49 years old. Although national guidelines recommend germline genetic risk evaluations for all patients with yCRC, multiple studies have shown suboptimal rates of guideline-recommended genetic evaluations. Methods: We conducted a pilot implementation study of a default genetic referral process for patients diagnosed with CRC between ages 40-49 from 1/2019-4/2022 at five hospitals in an academic health system. Patients previously referred to genetics were analyzed as a historical comparator cohort. In the intervention cohort, a research coordinator notified patients and their oncologists of their eligibility for a default genetic referral via an electronic patient portal message or telephone call, after which all patients who did not opt out within two weeks were referred for genetic counseling, testing, and result disclosure as per usual care. The primary outcome was feasibility, defined as a ≥60% referral rate; secondary outcomes included the proportion of genetic referrals that were scheduled, completed, and resulted in testing within three months of referral. Semi-structured exit interviews were conducted with a subset of patients and oncologists to assess attitudes toward the default genetic referral process. Results: We identified 128 patients with yCRC; 75 (59%) had previously been referred to genetics and were assigned to the historical cohort. There were no significant differences in sex, race, or ethnicity between the historical and intervention cohorts. All 10 patients with mismatch repair deficient tumors had previously been referred to genetics. Of the 53 patients in the intervention cohort, 49 (92%) were referred to genetics after one oncologist opted out on behalf of an international patient due to financial concerns and three patients requested to discuss with their oncologist before being referred. Of the patients who were referred, 38 (78%) were scheduled, 22 (45%) completed genetic counseling, and 13 (27%) underwent testing within three months of referral. Reasons for failing to complete the germline genetic risk evaluation process included lack of interest, competing priorities, communication/scheduling challenges, and failure to return saliva-based genetic testing kits. In exit interviews with 10 patients who completed testing and 10 oncologists, participants reported finding the default genetic referral process to be acceptable and feasible to implement. Conclusions: A default genetic referral process is feasible and results in a high referral rate for patients with yCRC, but subsequent scheduling, evaluation, and testing rates remain suboptimal. Multilevel implementation strategies are needed to address the patient, clinician, and system barriers identified in this study. Clinical trial information: NCT05018156.