The retail environment is an important determinant of food package redemption in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). The objectives of this study were to describe where Massachusetts WIC households redeemed their food benefits each month and monthly variations in benefit redemption depending on a household's most frequently used vendor type each month. These were cross-sectional and longitudinal analyses of administrative data provided by Massachusetts WIC. Monthly redemption data for 209,973 households shopping at approximately 1,000 unique vendors between January 2015 and August 2019 were analyzed. Outcomes were mean monthly percentage of households that relied on each vendor type when redeeming benefits and mean monthly percent redemption for each benefit category. For each month, households were classified as using 1 of 8 vendor types. The monthly percentage of households redeeming at each vendor type was calculated, as well as the monthly percent redemption for each benefit category by vendor type. The averages of these monthly percentages were computed for 2015 and 2019. Data from months when households did not redeem any benefits were excluded from primary analyses because it was not possible to determine their vendor type for that month. On average across months in 2019, the majority of Massachusetts WIC households (63%) relied on large vendors only (ie, superstores, supermarkets, and large grocery stores) when redeeming benefits, and 5% relied on small grocery or convenience stores only. Between 2015 and 2019, mean monthly reliance on small grocery and convenience stores decreased by 3.1 and 0.7 percentage points, respectively. Compared with other vendor types, households that redeemed benefits at superstores only had, in an average month, lower redemption levels for most benefit categories. For example, in the 2019 mean across months, percent redemption of breakfast cereal was 53% among households redeeming at superstores only compared with 74% for those redeeming at small grocery stores only. By contrast, households that relied on small grocery stores only had, in an average month, lower redemption levels for yogurt and cash value benefit compared with other vendor types; for example, in the 2019 mean across months, percent redemption of yogurt was 34% among households redeeming at small grocery stores only compared with 62% among those redeeming at supermarkets only. Results suggest that retail-based efforts to increase redemption should consider vendor-type reliance. Strategies to increase redemption may be especially important for WIC shoppers relying on superstores.