Area code

MD

United States geographic area code, in service since 1991-10-06. Part of the 410/443/667 overlay complex — ten-digit dialing required.

Split from 301. Created 443. Overlaid with 443, 667 .

Statusin service

Introduced1991-10-06

JurisdictionMD, US

Local dialing10D

Time zoneEastern

Last verified2026-09-17

Utilization 101% of assignable prefixes assigned As of 09/17/2026

0%800 of ~792 assignable NXX values (200–999 excl. N11)100%

Prefix-level assignment does not equal number-level exhaustion; thousands-block pooling extends capacity. First assignment on record 2001-04-18, most recent 2023-07-19.

Area codes serve rate-center geographies, not municipal boundaries. “MD” identifies the jurisdiction, not an exact city footprint.

Top assignees

Ranked by assigned prefixes · initial assignee ≠ current carrier

Largest initial assignees in area code 410
Rank	Assignee	Prefixes	Share
01	VERIZON MARYLAND, INC.	510	63.7%
02	CELLCO PARTNERSHIP DBA VERIZON WIRELESS - MD	53	6.6%
03	NEW CINGULAR WIRELESS PCS, LLC - DC	51	6.4%
04	MCIMETRO ACCESS TRANSMISSION SERVICES LLC - MD	45	5.6%
05	SPOK, INC.	28	3.5%
06	OMNIPOINT COMMUNICATIONS CAP OPERATIONS, LLC	22	2.8%
07	TELEPORT COMMUNICATIONS AMERICA, LLC - MD	15	1.9%
08	PAETEC ITEL, LLC	12	1.5%
09	LEVEL 3 TELECOM OF MARYLAND, LLC - MD	11	1.4%
10	MULTIPLE OCN LISTING	10	1.3%

Important: these are initial assignees from NANPA CO-code records — the carrier a prefix was originally assigned to. Because of number portability, the current serving carrier of any individual number may differ.

Change history

Recorded events for this NPA

2001-03-14 NPA 667 to Overlay NPAs 410 and 443 (Maryland) overlay
1991-10-06Area code 410 entered service (created from 301).

Planning letters & orders

Primary documents

NANPA planning letters for area code 410
Date	Document	Subject
2011-10-10	PL-427 ↗	NPA Code 667 to Overlay NPA Code 410/443 (Maryland)
2001-09-04	PL-299 ↗	Rationing in NPAs 410, 443, and 667 (Maryland)
1996-06-21	IL-96-06-008 ↗	NANP-Overlay of 410 (Maryland) Numbering Plan Area (NPA)
1990-12-28	IL-90-12-049 ↗	NANP - SPLIT OF THE 301 (MARYLAND) NUMBERING PLAN AREA (NPA)

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