Ninety-four people have been admitted to the hospital with the infection since the outbreak began on July 10 in the Bronx, the poorest county in the state.
The disease is spread by a bacteria, which has recently been discovered in the cooling towers of five buildings in the South Bronx area.
Officials said all those who died were older patients and had pre-existing medical conditions. Legionnaires' disease is not contagious and can be treated with antibiotics.
"We're optimistic that we've seen the worst of this outbreak and that our remediation efforts are having an impact," it said.
More From This Section
The disease, a serious pulmonary infection, is spread by bacteria that thrive in warm water, such as that found in hot water pipes, air-conditioning systems and industrial ponds.
Infections result from inhaling airborne droplets of contaminated water. The incubation period lasts two to 10 days.
Anyone in the Bronx with symptoms such as fever, coughing and shortness of breath are advised to seek medical attention immediately.
The disease takes its name from its first outbreak, in 1976, at a Philadelphia hotel where a meeting of the American Legion society was being held.