The area code 603 is located in Dover, New Hampshire.
Area code 603 serves all of Dover, New Hampshire, and the entire state. Dover sits in southeastern New Hampshire, near the Maine border, and anchors the Seacoast Region along with Portsmouth and Durham. As a historic mill city on the Cocheco River, Dover connects local homes, schools, and businesses with a single, statewide New Hampshire area code. When you see a 603 phone number, it can come from any corner of the Granite State—north to the White Mountains, west to the Connecticut River Valley, and east to the coast.
Established in 1947, area code 603 is one of the original North American Numbering Plan area codes and has remained the state’s only code ever since. That single-code status makes 603 a strong symbol of New Hampshire identity, from big cities to small towns. The code covers major destinations, including the state capital and popular tourist spots around lakes and mountains. It also ties Dover to nearby universities and hospitals, supporting daily life across the region.
Dover is one of New Hampshire’s oldest permanent settlements, dating back to the early 1600s, and today it blends history with a growing tech and education scene. The broader 603 area code links landmarks like Mount Washington, the White Mountain National Forest, and Lake Winnipesaukee under one statewide dialing identity. Many residents mark “603 Day” on June 3 as a fun nod to New Hampshire pride. For callers and businesses, that means a 603 number signals a genuine New Hampshire connection—whether you’re on the Seacoast, in the Lakes Region, or up in the mountains.
“Established in 1947 as one of the original NANP area codes.” — North American Numbering Plan Administrator (NANPA)