The health benefits of breastfeeding are well-documented, but rates of breastfeeding duration in the US fall below national targets - especially when mothers have less education, have lower incomes, are non-Hispanic Black, or live in nonmetropolitan areas. The Creating Breastfeeding Friendly Communities program was designed to promote breastfeeding and reduce disparities by implementing policy and practice changes in worksites from 2017 through 2023. The purpose of this evaluation was to determine whether the program was effective in increasing breastfeeding supports and addressing disparities. We used a 14-item tool to assess breastfeeding policies and practices at baseline and follow-up at each worksite. We used number of employees to determine worksite size, and we used worksite address to calculate social vulnerability of the community where each site was located and to classify rurality of the county where sites were located. We found significant improvements in the number and quality of breastfeeding supports available at participating worksites (N = 292 at baseline and follow-up). The program successfully reached worksites in socially vulnerable communities. Supports for breastfeeding increased in all worksite subgroups, but they increased less at worksites that were small or rural. The evaluation supports the effectiveness of worksite lactation programs and protective labor laws. Findings suggest that special attention must be given to worksites that are small, located in socially vulnerable communities, or rural counties, to support implementation and reduce disparities.