The U.S. safety net, which provides critical aid to households with low income, is composed of a patchwork of separate programs, and many people with low income benefit from accessing <1 program. However, little is known about multiprogram take-up, that is, participation conditioned on eligibility. This study examined individual and multiprogram take-up patterns and sociodemographic factors associated with multiprogram take-up of U.S. safety net programs. The Assessing California Communities’ Experiences with Safety Net Supports study interviewed Californians and reviewed their 2019 tax forms between August 2020 and May 2021. Take-up of safety net programs was calculated among eligible participants (n=365), including the Earned Income Tax Credit; Supplemental Nutrition Assistance Program; the Special Supplemental Nutrition Program for Women, Infants, and Children; and Medicaid. Multivariable regressions identified sociodemographic factors associated with take-up of multiple programs. Take-up was highest for Medicaid (90.6%) and lowest for Supplemental Nutrition Assistance Program (57.5%). Among people who received benefits from at least 1 other program, take-up ranged from 81.7% to 84.8% for the Earned Income Tax Credit; 54.4%-62.0% for Supplemental Nutrition Assistance Program; 74.3%-80.1% for Special Supplemental Nutrition Program for Women, Infants, and Children; and 89.7%-98.1% for Medicaid. Having a lower income and being younger were associated with concurrent take-up of Supplemental Nutrition Assistance Program and Special Supplemental Nutrition Program for Women, Infants, and Children. Among Supplemental Nutrition Assistance Program and Special Supplemental Nutrition Program for Women, Infants, and Children recipients, having higher income, being older, and being primarily English speaking were associated with Earned Income Tax Credit take-up.