According to Riverhead Town police, Daniel Locastro, 62, of Riverhead, was attempting to cross Main Street at the corner of Howell Avenue in a southerly direction when he was hit by a car heading westbound.
Police said the call came in at 5:02 p.m.; when they arrived at the scene, Locastro was lying in the roadway, "alive, but unresponsive, with shallow breathing."
Riverhead Police Lt. David Lessard said the man had "serious" injuries; the accident is still being investigated.
He was transported to Peconic Bay Medical Center by Riverhead Volunteer Ambulance Corp. He was later transferred to Stony Brook Hospital.
Barbara Guerin, 76, also of Riverhead, the driver of the 2001 Hyundai that struck the man, Lessard said, was not charged. Police said Locastro walked out into the travel portion of the roadway and was struck.
"She said she didn't see him," he said, adding again that the specifics of the accident were still under investigation.
Police said no charges are expected to be filed.