The dog, a silky male Yorkshire terrier-type, was found extremely matted and covered in feces and urine, according to a notification sent to the SPCA on Sunday.
He was in a cage on the side of Candlewood Road.
The dog was then brought to a 24-hour veterinary hospital, where he was believed to be near death and in need of aggressive medical attention.
Examinations revealed the dog was emaciated and had open sores on its body. It weighed only about 4 and a half pounds, according to Roy Gross of the SPCA.
Anyone with information is asked to call the Suffolk County SPCA at 631-382-7722.