The woman, who is older than 70, became ill on July 27, was hospitalized and is now recovering, according to a news release from the Nassau County Health Department.
Last year, Nassau County reported 16 confirmed West Nile virus cases and one death.
As of Tuesday, the federal Centers for Disease Control and Prevention said that 1,118 human cases had been reported nationally, including 41 deaths. The number of cases reported through the third week of August is the highest since 1999, when the virus was first detected in the county, the CDC said.
Nearly half of this year's cases have been reported in Texas, according to the CDC.
Five cases have been confirmed this year in New York City, with five more in the rest of the state, said a spokesman for the state Health Department. One person, in Onondaga County, has died, the county's website announced Monday.
So far this year, Nassau County has reported 58 mosquito samples as testing positive for the virus. Humans contract the virus from the bite of an infected mosquito.
The departments of health and public works "will continue their mosquito control efforts by inspecting breeding sites and, when indicated, conducting localized ground treatment to control mosquitoes that may be carrying West Nile virus," the release said.
One case has been confirmed in Suffolk County, health officials said.
Last year, Suffolk reported four confirmed cases of the virus and no deaths.