National Pollutant Discharge Elimination System (NPDES)

Urbanized Area Maps for NPDES MS4 Phase II Stormwater Permits

2010 Urbanized Areas (Newest Maps)

The universe of regulated small municipal separate storm sewer systems (MS4s) in urbanized areas expands every 10 years, according to the 1999 stormwater Phase II final rule. A “small MS4” is any MS4 not already covered under Phase I of the NPDES stormwater program. The expansion is based on the U.S. Census Bureau’s definition of “urbanized area.”

Census Bureau maps of 2010 urbanized areas can be used by:

  • permitting authorities to determine which new MS4s are located in each 2010 urbanized area and require coverage under an MS4 permit,
  • regulated MS4s to determine which parts of their jurisdiction are located in a 2010 urbanized area where the MS4 program applies, and  
  • others interested parties to access regional PDF maps that depict urbanized areas across the United States.

Each urbanized area folder contains a series of Portable Document Format (PDF) files:

  • The first PDF contains a reference map and additional detailed maps.
  • The remaining PDFs are individual copies of the detailed maps.

Note: The folders for some smaller urbanized areas contain only one map.

The urbanized area and urban cluster both appear in green on the reference maps, which makes it difficult to distinguish them. However, the urbanized area labels appear in regular font while the urban clusters are slightly italicized. EPA’s small MS4 program applies in the urbanized areas.

The Census Bureau provides additional helpful information:

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2000 Urbanized Areas (Older Maps)

EPA developed a set of digitized maps for each urbanized area as defined by the 2000 U.S. census. The 2000 maps have been superseded by the new 2010 census data, but are still available upon request.

To obtain copies of the maps:

  1. Email your request and  
  2. include the state and urbanized area that you are requesting.

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