The woman was walking alone on a hiking trail near the park's Hendrickson Avenue entrance about 11:10 a.m. when she was attacked, New York State Park Police Chief Richard K. O'Donnell said.
The victim described her attacker to police as 29 to 35 years old, 5-foot-8 to 5-foot-9, with a thin build.
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He had short hair with braids on the side and was wearing black pants and a white T-shirt.
Nassau police, State Park Police and New York State Police canvassed the park and surrounding neighborhood with police dogs and flew helicopters overhead, O'Donnell said.
O'Donnell described the attack, in broad daylight, as "very unusual," with no recent reported suspicious activity at the park.
"We would like to hear from people who might have been in the park around that time who may have seen something suspicious," O'Donnell said.
Anyone with information can call State Park Police at 631-321-3700.