Every Michigan Area Code, and the Split Tree Behind Detroit's Newest

All 13 Michigan area codes

Michigan's 13 area codes trace back to just three original codes assigned when the North American Numbering Plan launched in 1947. Seven descend from Detroit's 313 alone; the rest split off from Grand Rapids's 616 or Lansing's 517, as the table below shows; see how area codes actually work for what "split" and "overlay" mean in practice. North Carolina is about to go through the same kind of addition Michigan just finished: a new overlay code is on the way for the state, following the same pattern that brought Michigan's newest code, 679, online in November 2025.

Detroit's 313 grew into seven of Michigan's 13 codes

313 covered the entire Detroit metro area on its own from 1947 until 1993, when the state split off 810 to cover Flint, Port Huron, and the rural Thumb region northeast of the city. 810 was itself split twice more within a decade: 248 broke off in 1997 to cover Oakland County, and 586 followed in 2001 for Macomb County. Oakland County then ran out of numbers under 248 alone and got a second, overlaid code, 947, in 2002. Detroit's other direct split, 734, peeled off Ann Arbor and Ypsilanti in 1997.

313 itself kept its original Detroit-Dearborn-Grosse Pointes footprint the whole time, and by the early 2020s was projected to run out of available numbers again, this time without room left to split off a new geographic area. Michigan's regulator chose an overlay instead: 679 was reserved for the same territory 313 already covered, and went into service for new lines on November 7, 2025. Between the two of them, the seven codes descended from 313 (313, 810, 248, 586, 947, 734, and 679) now account for just over half of the state's total.

One metro area's original code eventually accounting for the majority of its state's total isn't unique to Michigan: California's own area code history shows the same pattern at a larger scale, where Los Angeles alone now runs on seven area codes, all descended from a single 1947 code, 213.

Grand Rapids and Lansing split off the rest

616 covered Grand Rapids and the rest of southwestern Michigan from 1947 until 1961, when the Upper Peninsula split off as 906, geographically Michigan's largest area code by far, despite covering one of its smallest populations. 616 split twice more after that: 231 broke off the northwestern Lower Peninsula (Traverse City, Muskegon) in 1999, and 269 took Kalamazoo and Battle Creek in 2002, leaving 616 itself with just the immediate Grand Rapids area.

517 has had the quietest history of Michigan's three originals: it covered Lansing and the south-central part of the state from 1947 and split only once, handing Bay City, Saginaw, and Alpena to the new 989 code in 2001. Unlike 313 and 248, neither 517 nor 616 has needed an overlay yet; both still run on a single area code today.

679 is under a year old, and it changed how Detroit dials

The Michigan Public Service Commission set 679 in motion after an early-2020s projection put 313's number exhaustion in the third quarter of 2025, the estimate that triggered the overlay case. That exhaustion date has since been pushed back: thousands-block number pooling and other conservation measures extended 313's runway, and the commission's own 2025 filings put the current projected exhaustion date in late 2027. The overlay itself went ahead on its original schedule regardless. Because 313 already covered a fully built-out urban area with no adjacent territory left to split off, the commission chose an overlay rather than a geographic split, meaning existing 313 numbers stayed exactly as they were, and new phone lines in the same area became eligible to receive 679 numbers once the overlay went into service.

The overlay came with a dialing change that arrived before the new area code itself did: starting April 7, 2025, callers within the 313 area were asked to begin practicing 10-digit dialing, and it became mandatory for all local calls on October 7, 2025, a full month before 679 numbers were actually assigned, starting November 7, 2025. That sequencing is standard for NANPA-coordinated overlays: the dialing change has to be in place first, or a new 10-digit number and an old 7-digit one in the same area code could collide.

What still dials on three digits, and what needed reprogramming

The overlay didn't touch every kind of number in the 313/679 region. Emergency and community short codes kept their original length: 911 and 988 are still three digits, and so are 211, 311, 411, 511, 611, 711, and 811 anywhere they're already in service. None of those grew to 10 digits when 679 went live.

What did need attention, per the press release NANPA issued announcing the mandatory-dialing date, was anything still programmed to place calls using the old 7-digit format. Its list of examples runs well beyond phones: life-safety systems, medical alert devices, alarm and security systems, fax machines, automatic gates, ankle monitors, speed dialers, and call-forwarding or voicemail settings all needed a check, alongside the more obvious cases, like updating a business's printed stationery or a personal check to show the area code next to the number. Most equipment sold in the past decade already dials 10 digits by default, but NANPA flagged older hardware specifically, and told anyone unsure how a device was configured to contact its medical-alert or security provider directly rather than assume it still worked.