CARY, N.C. — People who live in south Cary should get used to the number 27518. It will soon be their new ZIP code, and it will be the fifth new ZIP code in the Triangle in the past five years.

For years, homeowners in Windermere and Cotswold neighborhoods technically have lived in south Cary, paid Cary taxes, and received Cary services. But all their bills, packages, and letters come to Apex mailing addresses with the ZIP code of 27539. Windermere resident Cindy Bunce said they have often paid out-of-town fees for Cary sports and other activities.

"It's confusing, because we try to tell people we actually live in Cary, but we have an Apex mailing address," said Bunce. "And we're outsiders to the rest of the Cary community."

On July 1, that will change. The neighborhoods will become part of the new Cary ZIP code.

Cary Postmaster John Thompson said some ZIP codes are getting overloaded, creating delivery efficiency problems.

Next month, around 7,000 postal customers south of U.S. 64 in the 27511 ZIP code must get used to a new number. Most already have a Cary mailing address, but they will still have to change to 27518.

"They've already called me and complained about changing," said Thompson. "(They've said,) 'This is all I've known for 30 years.' As I explained to them, please have patience with us."

Sometimes, it's not just about convenience. A mailing address can add or subtract property value.

For example, the new Martha Stewart development is in Cary's annexed land, yet the mailing address is Morrisville. Conversations are under way on what the ZIP code for the development should be, and whether homeowners should call Cary or Morrisville home.

Blame it on growth, but thousands will soon get new addresses without moving.

Thompson warned residents not to change their ZIP code until July 1, or they may not get their mail. After that, South Cary residents will have one year to transition to 27518.