I am the ancestor of Asa Porter and Sarah Marr. She was supposedly born in 1771 in Digby, NS.
His parents were William Porter and Mary Bachelder who originally lived in Salem MA, moved to Danvers, Ma (which was originally a part of Salem). I originally believed Asa was the son of Josiah Porter and Sarah Bradstreet. Josiah was William's son and Asa would be the grandson. However, the library in woburn informed me ther is no Asa Porter listed as being the son of Josiah.
Your request for information on the Porter family has been forwarded to me. I have found in our archives a paper that was written in 1976 by two members of the Porter family which may be of interest to you. It states that Josiah was the 6th of 8 sons born to William Porter and his second wife, Mary Batchelder Kettle of Beverly, MA. (Beverly Town Records show her to be a widow named Mary Kittle.) The paper states that deed records of Lebanon, Conn. indicate that Josiah Porter purchased property there in 1750 and established a clothing business. Four children were born in Lebanon including Asahel in 1751, he was the second child and eldest son of Josiah, and Dudley on March 13, 1752-53, he was the second son of Josiah. It also speaks of Josiah Porter, 2nd, the youngest son of Josiah who was born in Woburn, MA on July 25, 1759. (I cannot confirm that as the Woburn Record of Births lists the first Porter being born in Woburn in 1846.)
Dudley and Josiah are listed as soldiers in the Massachusetts Soldiers and Sailors of the Revolutionary War. Asahel was killed at Lexington Green but was not a soldier at the time. The story is that he was accompanying his friend, Mr. Richardson, to market early on that April morning when they encountered the British soldiers who were marching to Lexington and Concord. The two were taken prisoner and released as they approached Lexington Green. They were told to walk away and not to run. Supposedly, Asahel ran and was shot in the back. Could this have been the "shot heard round the world" that started the fighting? We may never know.
This paper does not mention an Asa Porter. There are several Asa Porters listed in the Mass Soldiers and Sailors of the Revolutionary War, but none are listed as being from Woburn and several have no town listed at all. So it is hard to determine if one is the Asa you are looking for.
I also checked the Beverly Town Records. The only Asa Porter listed as being born in Beverly is the son of William,jr. and Lydia, baptized on July 13, 1740. The Beverly Town Records show that William Porter, jr. married Lydia Batchelder, both of Salem, on July 5, 1733.