Metro 4 represents seventeen southeastern local (city, county, and metropolitan) air pollution control agencies located in the area designated by the United States Environmental Protection Agency as Region 4.

The Metro 4 agencies are located in:

• Huntsville, Alabama
• Jefferson County, Alabama (Birmingham area)
• Broward County, Florida (Fort Lauderdale area)
• Hillsborough County, Florida (Tampa area)
• Jacksonville, Florida
• Miami-Dade County, Florida
• Orange County, Florida (Orlando area)
• Palm Beach County, Florida (West Palm Beach area)
• Pinellas County, Florida (St. Petersburg/Clearwater area)
• Louisville, Kentucky
• Forsyth County, North Carolina (Winston-Salem area)
• Mecklenburg County, North Carolina (Charlotte area)
• Western North Carolina (Asheville area)
• Chattanooga-Hamilton County, Tennessee
• Knox County, Tennessee (Knoxville area)
• Memphis-Shelby County, Tennessee
• Nashville, Tennessee