Boston residents who say they live in Hyde Park despite a zip code placing their homes in Mattapan say they hope to have a response from the US Postal Service next month.

Barbara Hamilton, a member of the East River Neighborhood Association, spearheaded the quest for the change, an effort that has been underway since 2009 and affects 1,600 addresses. She said she gathered 800 signatures, which were submitted to Postal Service officials last year.

According to the neighborhood association, the change in zip code to Mattapan’s 02126 from Hyde Park’s 02136 occurred in the 1980s. In a 2010 letter to Boston’s postmaster, James Holland, the association said the Mattapan zip code has led to a $100,000 difference in home median value, refinancing and appraisal disparities, confusion in receiving mail, and increased costs for car insurance.

“GPS uses the zip code,” Hamilton said. “The insurance companies use the zip code. So when your zip code changes, everything else is thrown out of whack.”

The effort has received support from Mayor Thomas Menino, Congressman Michael Capuano, and District 5 City Councillor Rob Consalvo, who represents Hyde Park and Mattapan.

Consalvo and Hamilton are quick to add that they don’t intend to slight Mattapan in their pursuit of the zip code change. “It’s not a matter of us versus Mattapan,” Hamilton said.

Consalvo said the deeds of the Hyde Park houses with a Mattapan zip code place them in Hyde Park, and points to a map that uses Greenfield Road as a dividing line. “These are all houses that are clearly in Hyde Park.”

A map from the annexation of Hyde Park is the “smoking gun,” Consalvo said, because it shows those streets belong in the neighborhood. According to the city’s website, Hyde Park was incorporated as a town in 1868 and annexed to Boston in 1912.

Postal Service spokesman Dennis Tarmey said Consalvo and residents have made a “strong case” and a meeting between parties was expected this week. If the change is approved, it could be implemented by July.

In a letter dated March 30, 2011, the postmaster acknowledged that some of the addresses listed are “already addresses that are delivered” out of Hyde Park’s post office. “We have so much evidence in our favor,” Consalvo told the Reporter. “They’ve stood up to the plate; they’ve agreed to hear the case.”

Dorchester and Mattapan residents are familiar with shifting boundary lines: Over the last several decades, city planners have frequently moved Dorchester’s traditional boundaries into Roxbury and Mattapan, to the chagrin of residents.