Marijuana use among U.S. college students is the highest since the mid-1980s. Because knowledge about marijuana and confidence in the knowledge are related to changing marijuana laws and marijuana-related messages ubiquitous in college students' information environment, we examined their relationships with use. The Structural Equation Modeling method was used to analyze the relationships using survey responses from 249 college students in an adult-use marijuana legal state. Marijuana health knowledge was related to less use, and law knowledge was related to more use. Both relationships were mediated by perceived risk. Confidence in knowledge was related to more use directly as well as indirectly via lower peer disapproval and lower perceived risk. Among various marijuana message channels, peers were the most influential, contributing to lower health knowledge and higher confidence in knowledge.