The U.S. Environmental Protection Agency (EPA) is finalizing clarifications to its National Pollutant Discharge Elimination System (NPDES) Stormwater Phase II regulations due to recent changes made by the Census Bureau. The changes to EPA's regulations are limited to clarifying that the designation criteria for small municipal separate storm sewer systems (MS4s), which have been used since the promulgation of the regulations in 1999, will remain the same. These clarifications are necessary due to the Census Bureau's recent decision to discontinue its practice of publishing the location of "urbanized areas" along with the 2020 Census and future censuses. The clarifications in this final rule replace the term "urbanized area" in the Phase II regulations with the phrase "urban areas with a population of at least 50,000," which is the Census Bureau's longstanding definition of the term urbanized areas. This change allows NPDES permitting authorities to use 2020 Census and future Census data in a manner that is consistent with existing longstanding regulatory practice.