Rural adolescents are at high risk for firearm-related injury, yet most existing prevention efforts are informed by research conducted in urban areas. Despite the need to account for rural perspectives, few studies have investigated the unique social ecological context of firearms for rural adolescents or have directly engaged with rural adolescents to understand their views on firearm use. To describe rural adolescents' firearm behaviors and perceptions of firearm-related social norms within their communities, peer groups, and families. This cross-sectional study used a convergent mixed-methods design and involved a community-based participatory research approach. Participants comprised 93 adolescents residing in rural Washington state and enrolled in a county or tribal reservation 4-H youth development program as an intermediate or senior age-level grouping (ie, aged 12-19 years). Adolescents completed a survey and participated in a semistructured focus group or interview between September 1, 2021, and September 30, 2022. Data were analyzed using descriptive and thematic analysis. Individual handgun behavior and peer, family, and community perceptions of firearm-related social norms. The sample included 93 adolescents (mean [SD] age, 15.7 [1.7] years; 49 female participants [52.7%]). Approximately half of participants (52 [55.9%]) had carried a handgun at some point in their lives, with a mean (SD) age at first carry of 10.9 (3.1) years. Primary themes across quantitative and qualitative data focused on social norms (specifically, acceptable and unacceptable ways to engage with firearms, reasons for carrying firearms, and places to carry a firearm). In this cross-sectional study, rural adolescents in 4-H programs generally understood acceptable and unacceptable firearm carrying behaviors, which aligned with state laws. Findings provide context for rural adolescent behaviors such as carrying a firearm predominantly for prosocial reasons (hunting, recreation, and sport) and adult behavior such as carrying for protection of person and personal property. Understanding firearm-related social norms in rural communities holds implications for firearm injury prevention efforts, especially related to enhancing training, developing norms-based prevention approaches, and tailoring efforts to rural settings.