Janice,
If you are still watching the board, I believe the Petrus you are looking for is my 5th Great Grandfather Petrus David Demarest, son of David Benjamin Demarest, # 5-180 in the Demarest Family genealogy. Here is what I know:

5-180 PETRUS DAVID DEMAREST born May 13, 1761 in Schraalenberg, died June (July) 16, 1832, married (6-98) Sara Demarest born June 17, baptized June 22, 1760 in Scraalenberg, died April 26, 1844, buried Broadalbin, NY. Daughter of (5-47) NICLAES DEMAREST and (4-102) ELSIE DEMAREST His will was dated February 26, 1816 probated June 24, 1832 and is at Johnstown, NY 2-72. Records have been found indicating Petrus’ service as a Private in the Bergen County Militia in the Outwater Company. Received for his service a land grant in Broadalbin, NY.

R/
Bob Demarest, Rome, NY