Universal public prekindergarten programs have been expanding in recent years, but not all eligible families apply to these programs, for reasons that are not well understood. Using two cohorts of students (N = 8,391) enrolled in Boston Public Schools, we use geographic information systems to combine administrative records with census data to compare the student-, neighborhood-, and school-level characteristics of kindergarteners who did and did not apply to the Boston Public Schools prekindergarten program. We find that nonappliers are more likely to be non-White (SD = 0.27), low income (SD = 0.11), and dual language (SD = 0.58), particularly those who did not attend any other prekindergarten program. We find similar differences at the neighborhood and school levels. Our study provides some of the first descriptive information on the sociodemographic characteristics and spatial distribution of families who opt out of applying to universal prekindergarten programs. Findings may inform recruitment strategies to promote equitable and universal prekindergarten enrollment.