Although the number of infants diagnosed with neonatal opioid withdrawal syndrome (NOWS) and the number of infants entering foster care have increased substantially in the US since 2009, analyses exploring their relationship are lacking. Using data from 580 US counties in eight US states from the period 2009-17, we examined the association of county rates of NOWS and county-level characteristics with infant foster care entries. In adjusted analyses, every one diagnosis of NOWS per ten births was associated with a 41 percent higher rate of infant foster care entry, and rural county residence was associated with a 19 percent higher rate of infant foster entry. A higher employment rate was associated with lower rates of infant foster care entry both overall and in urban counties when we stratified by rurality. These findings suggest that policy makers could use information about county characteristics to better target funding to support opioid-affected families at risk for foster care involvement.