Background Colorectal cancer (CRC) is the first commonest diagnosed cancer in men and the fourth commonest in women in Ethiopia. Awareness of CRC and associated factors is crucial in the prevention of CRC. However, there have not been studies about the awareness of CRC and associated factors among adult patients in Ethiopia. Therefore, the study aimed to assess the awareness of CRC and associated factors among adult patients in Jimma, South-West Ethiopia, 2020. Methods This institution-based cross-sectional study design was conducted among 422 adult patients. The study respondents were recruited by a systematic random sampling method. The Cancer Awareness Measure questions were used to measure awareness of CRC of adult patients. Descriptive and logistic regression analyses were conducted. Results More than half (57.6%) of respondents had low-level awareness of CRC. Respondents who were females (adjusted odds ratio [AOR] = 1.86; 95% CI: 1.26, 2.75), who are residing in urban areas (AOR = .45; 95% CI: .30, .67), who had a monthly income of 3000 Ethiopian Birr and above (AOR = 4.72; 95% CI: 3.11, 7.15), who heard about CRC (AOR = 4.48; 95% CI: 2.90, 6.93), who get information through social media about CRC (AOR = 2.51; 95% CI: 1.18, 5.37), and who had a family history of CRC (AOR = 3.27; 95% CI: 1.45, 7.36) had a high level of awareness of CRC, while those who cannot read and write (AOR = 2.83; 95% CI: 1.49, 5.37) and learn elementary school (AOR = 2.12; 95% CI: 1.15, 3.93) had a low level of awareness of CRC. Conclusion This study indicated that awareness of CRC of adult patients was inadequate. Adult patients’ gender, residency, level of education, monthly income, heard about CRC, sources of information about CRC, and a family history of CRC were found to be independent predictors of the awareness of CRC. Therefore, there is a need for health education and awareness campaigns for promoting awareness of CRC of adult patients, and the government should develop policy on CRC prevention and screening program.