Area Code Atlas

Area code 203 established as one of the original North American Numbering Plan area codes

Area code 203 was established in 1947 as one of the original North American Numbering Plan area codes, covering the entire state of Connecticut. It served as the sole area code for Connecticut until 1995, and initially included counties such as Fairfield and New Haven.

Area code 860 split from 203

In 1995, area code 860 was introduced for the majority of Connecticut, reducing the area served by 203 to the southwestern part of the state. The split was implemented to provide additional numbering resources as demand increased.

NANP-SPLIT OF 203 (CONNECTICUT) NUMBERING PLAN AREA (NPA)

NPA 860 split from 203

Area code 860 was created on August 28, 1995, when Connecticut was divided into two numbering plan areas. The new code covered the majority of the state outside the southwestern region, while 203 was reduced to serve the southwestern portion including Fairfield County (except Sherman), New Haven County, and part of Litchfield County.

Extraordinary NPA-Specific Jeopardy Conservation Procedures Announced for Connecticut NPAs 203 & 860

Overlay 475 proposed for NPA 203

The Connecticut Department of Public Utility Control proposed an overlay plan for area code 203.

Overlay of 475 on 203 ordered

On September 22, 1999, the Connecticut Department of Public Utility Control ordered the overlay of area code 475 on the existing 203 area. This decision was made to address the projected exhaustion of available numbers in the 203 region.

NPA 475 overlay on 203 announced

NPA 475 To Overlay NPA 203; NPA 959 To Overlay NPA 860 (Connecticut)

NPA 475 overlay on 203 announced

NPA 475 to Overlay NPA 203; NPA 860 10-digit dialing (Connecticut)

Mandatory ten-digit dialing implemented for all Connecticut area codes

On November 14, 2009, mandatory ten-digit dialing was implemented statewide in Connecticut in preparation for the 475 overlay on 203 and the planned 959 overlay on 860. This change was part of the broader transition involving area codes 203, 475, 860, and 959, supporting the introduction of new overlay codes, including 959 for the 860 region.

NPA 475 overlaid on 203

Area code 475 was activated as an overlay on the 203 region on December 12, 2009. The overlay provided additional numbering resources for southwestern Connecticut without requiring existing numbers to change. This overlay was first proposed by the Connecticut Department of Public Utility Control in August 1999.