Cellphone provider T-Mobile has begun construction on a new tower near Bay Avenue and 11th Street in Ronkonkoma, even as some local residents and a Suffolk County legislator said they opposed it.

The announcement came Wednesday afternoon during a “pre-construction” meeting with residents at the site. The project, which began Thursday, is expected to take one month to complete, T-Mobile spokesman Paul LaPasota said.

About 20 Ronkonkoma residents were there to hear the announcement. Most said they are opposed to construction of the tower.

“Absolutely I don’t want it erected. It’s 50 feet from my house,” said Kurt Johnson, 51. “It has no business being where it’s put.”

Suffolk County Legis. Tom Cilmi (R-Bay Shore) told a group of residents that he is opposed to the tower. Part of his legislative district includes the site.

“I fought against this,” he said. “Believe me, nobody fought harder than I did.”

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T-Mobile, of Bellevue, Washington, has struggled the past five years getting the project off the ground, and had filed a federal lawsuit against National Grid, the Long Island Power Authority and PSEG Long Island seeking injunctions to prevent the utilities from “further interference” in the project.

That suit was settled and filed in court Nov. 12, allowing construction to proceed.

PSEG previously had said it would not allow the project to move forward until T-Mobile had the “full support of the community.”

Deborah O’Brien, who has lived near the site for 30 years, said she is afraid the tower will affect her health. And Johnson said he is worried about medical implications and a decrease in property values.

At the meeting, T-Mobile officials reiterated that the tower will be constructed, adding that issues from the lawsuit would not be discussed.

“We’re not going to be revisiting details of the lawsuit. That issue has already been resolved. We’re just moving forward,” said T-Mobile spokesman Viet Nguyen in a phone interview.