BACKGROUND: Participation in the US Department of Agriculture's summer meals program is consistently lower compared to National School Lunch Program (NSLP) participation, even though the programs target the same population of children. The purpose of this study was to elucidate reasons for participation and nonparticipation in the summer meals program. METHODS: A nationally representative sample of 4688 households with children ages 5 through 18 years living near a summer meals site in 2018 completed a survey about their reasons for participation or nonparticipation in the summer meals program, features that would help nonparticipants to attend, and household food security status. RESULTS: Almost half of all households living near a summer meal site were food insecure (45%) and most (77%) had incomes at or below 130% of the federal poverty level. Most participant caregivers (74%) sent their children to summer meal sites for the free meals, while 46% of nonparticipant caregivers said they did not attend because they were unaware of the program. CONCLUSIONS: Despite a high level of food insecurity among all households, the most reported reason for not attending the summer meals program was unawareness of the program. These findings highlight a need for better program visibility and outreach.