Pulse oximetry screening of newborns detects critical congenital heart disease (CCHD). Rural birth location is known to affect timing and management of when infants with CHD undergo surgery, but its association with CCHD screening is unknown. We assess the relationship between rural location and postnatal CCHD diagnosis and describe lesion-specific modes of diagnosis. Data were abstracted from medical records at 2 cardiac surgery centers in Washington state. Infants with CCHD, defined as CHD requiring either cardiac intervention or resulting in death at <1month of age, born between July 2015 and June 2020, were included and classified by method of identification. Patient home ZIP codes were used to determine rural location. We included 561 newborns with CCHD; 35% were diagnosed postnatally. Predominant postnatal mechanisms of identification (n=194) included symptomatic before CCHD screening period (56%), CCHD screening (22%), and symptomatic after false-negative screen (15%). Postnatal diagnosis rate increased with degree of ruralness (48% in small rural/isolated regions vs 32% in urban regions; P=.01) and incidence of undiagnosed CCHD at birth increased with lower nursery levels (5.5/10000 live births in nursery level 1 vs 2.1/10000 live births in level 4). CCHD screening identifies 22% of postnatally diagnosed CCHD and 7% of cases overall in our region. Postnatal diagnosis is more common in rural regions. The incidence of undiagnosed CCHD at birth increases with decreasing nursery levels. This study supports the value of CCHD screening in routine newborn care, especially in rural areas and hospitals with lower nursery levels.