Background: Inappropriate solid waste management produced in the course of human activities has serious problems for the environment that adversely affect the health of the human population. Thus, towns and cities in developing countries like Ethiopia face environmental health and aesthetic problems resulting from improper management of solid waste disposal. Uncontrolled waste management may also contribute to the transmission of communicable diseases from different systems as well as encourage fly breading, which has nuisance effects in addition to disease transmission. Objective: To assess knowledge, attitude, and practice of solid waste management systems in households in Darge sub-city, East Wollega Zone, Oromia, Ethiopia. Methods: A community-based cross-sectional study was conducted using systematic random sampling techniques from February 1st to February 15th, 2022. Data was collected from 278 households using a structured interviewer-administered questionnaire. After data collection, data analysis was performed using SPSS computer software version 22.0. Results: The study showed that 67.3% had good knowledge, 65.86% had a positive attitude, and 63.3% had good practice in solid waste management (SWM). Among the households, 12.6% and 42.1% dispose of solid waste in open fields and open disposal pits, respectively. The perceived reason for improper solid waste disposal was a lack of awareness (55.4%) and a shortage of a place for solid waste disposal (30.6%). Conclusion: The knowledge, attitude, and practice of households in the study area need improvement according to standards for towns and sub-cities. Increasing knowledge, changing attitudes, and improving practice in SWM using the existing structure are recommended.