Understanding long-term impacts is essential to knowing whether an Extension program is achieving its goals. I describe a process for long-term program evaluation, using evaluation of the Utah Master Naturalist Program (UMNP) as a successful example. Surveys revealed that the UMNP had impacts on participants up to 10 years after program completion. The UMNP is achieving its goal of promoting stewardship through fostering a deeper connection to nature, encouraging lifelong learning, increasing stewardship feelings and activities, and providing effective professional development. Further long-term evaluation efforts will focus on quantifying behavior change. Overall, the UMNP evaluation process and results underscore the criticality of conducting long-term evaluation to understand lasting impacts of Extension programs.