Objectives: The Inter Tribal Council of Arizona, Inc (ITCA) Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) provides nutrition services for families by partnering with local vendors. In 2009, the US Department of Agriculture (USDA) instituted the WIC Vendor Cost Containment Final Rule, which required WIC programs to group vendors with similar characteristics. USDA issued guidance for evaluating and constructing vendor peer grouping systems in 2017. We constructed vendor peer groups using USDA recommended methods. Methods: We used ITCA WIC vendor and redemption data to construct composite variables for mean food basket cost as the outcome in linear models using the following predictors: business model, Supplemental Nutrition Assistance Program (SNAP) store type, WIC total sales, number of Universal Product Codes (UPCs) redeemed, number of cash registers, store square footage, rural–urban commuting area codes, 2010 Frontier and Remote (FAR) area codes, distance to the closest interstate in miles, and urban or nonurban location. We developed an ITCA WIC vendor peer group system. Results: We examined 146 ITCA WIC vendors. Final complete vendor peer groups for ITCA WIC in linear regression models included SNAP store type ( P < .001), number of cash registers ( P < .017), and FAR codes ( P < .001). FAR codes were important, while other geography measures were not. Conclusions: Using vendor peer groups can improve cost containment measures and the integrity of WIC services. Other WIC programs can use FAR codes as a USDA-required geography measure for local vendor peer group evaluations.