Background: During the 1920s and early 1930s, U.S. fertility declined overall but with large regional variations. Changes in foreign born populations explain only part of this. Differences in public health and poverty relief programs may further help explain these declines because of their potential impact on fertility determinants, in particular on breastfeeding and child mortality. Objective: We investigate whether public health investments in child health (conservation of child life programs) and poverty relief (outdoor care of poor or charity for children and mothers) affected fertility for U.S. cities over 100,000 persons between 1923 and 1932. Methods: We analyze data covering 64 cities between 1923-1932 that include birth information from the U.S. Birth, Stillbirth and Infant Mortality Statistics volumes and city financial information from the Financial Statistics of Cities volumes. Time and city fixed-effects models are used to identify the impact of public investments on fertility. Results: Fixed effects estimates indicating the conservation of child life programs explain about 10 percent of the fertility change between 1923 and 1932. Outdoor care of poor did not seem to be related to fertility. Investments in charity for children and mothers were associated with fertility increases, possibly because poorer areas experienced relative increases in both higher fertility and charitable spending. Conclusions: Public spending on child health was strongly related to decreasing fertility in the U.S. during the 1920s, possibly because of increased breastfeeding and decreased child mortality. This leads to a better understanding of the 1920s fertility decline and highlights how public policy may affect fertility.