New Hampshire Gazetteer
The 603 area code is used by SOME cities and towns in these Counties:
| Belknap County | Cities & Towns | ZIP Codes | Features |
| Carroll County | Cities & Towns | ZIP Codes | Features |
| Cheshire County | Cities & Towns | ZIP Codes | Features |
| Coos County | Cities & Towns | ZIP Codes | Features |
| Grafton County | Cities & Towns | ZIP Codes | Features |
| Hillsborough County | Cities & Towns | ZIP Codes | Features |
| Merrimack County | Cities & Towns | ZIP Codes | Features |
| Rockingham County | Cities & Towns | ZIP Codes | Features |
| Strafford County | Cities & Towns | ZIP Codes | Features |
| Sullivan County | Cities & Towns | ZIP Codes | Features |
