ObjectiveTo 1) define the number and characteristics of NICUs in the United States (US) and 2) identify hospital and population characteristics related to US NICUs.Study designCohort study of US NICUs.ResultsThere were 1424 NICUs identified in the US. Higher number of NICU beds was positively associated with higher NICU level (p< 0.0001). Higher acuity level and number of NICU beds related to being in a children’s hospital (p< 0.0001;p< 0.0001), part of an academic center (p= 0.006;p= 0.001), and in a state with Certificate of Need legislation (p= 0.023;p= 0.046). Higher acuity level related to higher population density (p< 0.0001), and higher number of beds related to increasing proportions of minorities in the population up until 50% minorities. There was also significant variation in NICU level by region.ConclusionsThis study contributes new knowledge by describing an updated registry of NICUs in the US in 2021 that can be used for comparisons and benchmarking.