The U.S. Department of Agriculture’s Cooperative Extension System (Extension) is available in every state and territory, with trained health professionals assigned to each county within the system. The mission of Extension is to translate research to practice in community settings. In 2014, the term “physical activity”, current physical activity behaviors of Americans, objectives for improved outcomes, was added to the Farm Bill, encouraging Extension professionals to affect physical activity participation for a large proportion of Americans. The purpose of this manuscript is to describe Extension and provide case studies on physical activity promotion within this setting. Three case studies are presented that reflected both direct and indirect physical activity promotion across different target audiences. Direct physical activity promotion through Extension was operationalized as interventions that included an in-person physical activity component or specific physical activity outcome. Indirect physical activity promotion included interventions that aimed to facilitate physical activity (e.g., policy, environmental changes, connecting community members with programs sponsored by different entities). One case study is based on an integrated research–practice partnership approach to improve the compatibility of an evidence-based intervention within the Extension system. A second case study indicates long-standing physical activity promotion efforts through direct education for older adults, a toolkit for integrating physical activity into elementary school settings, and an environmental assessment for physical activity within schools. The third case study reports on an overarching initiative to promote physical activity participation in early childhood through direct education, policy funding and support, and community campaigns. There are several ways to partner with the land grant system of Extension to promote programs, policies, and practice that support physical activity participation.