Police arrived at the crash at Our Lady of Mercy Church, 500 South Oyster Bay Rd., about 4:40 p.m.
Detectives said a 70-year-old unidentified woman was driving a 2002 Subaru on church grounds when she hit Rose Tantillo, 84.
Tantillo was taken to a hospital where she was pronounced dead at 5:26 p.m., police said.
Detectives said there is no criminality in the crash. The vehicle was impounded for brake and safety checks, police said.