When a parent has another child with a new partner, a significant effect on parents and children is likely, making factors associated with multiple-partner fertility of interest to policy makers. For single mothers, one potential policy-relevant factor influencing their subsequent fertility with a new partner is child support income. However, the direction and magnitude of any effect is not well-established. This study documents the simple negative relationship between child support and nonmarital fertility with a new partner in our sample of low-income unmarried mothers. We then take advantage of a policy experiment that resulted in randomly assigned differences in child support income to investigate its effects. We find no support for a negative causal relationship between child support receipt and nonmarital fertility with a new partner, instead finding suggestive evidence that mothers with more child support income are slightly more likely to have a subsequent nonmarital birth with a new partner.