If you will contact me directly, I can share with you a good deal more of the information that I have.(I believe my account here is set up so that you can see my email.)
The answer to your question lies in the Vital Records of Baldwin Maine for the late 1700's into the early 1800's. These are maintained on microfiche at the Maine state archives in Augusta. I've seen the records and have copies of the pertinent page(s).
In a nutshell: David Brown and his brother Ephraim were given a parcel of land on the western shores of Sebago Lake, by their father Capt. David Brown, of Concord, MA.Born in Concord, the boys moved up there around 1789/90, and lived there balance of their lives in what is today Baldwin, ME.John B. Brown was the second son of David and Esther, and their first child born after moving to Baldwin. In 1824, Ephraim, then the Baldwin town clerk, officially recorded the names and birth dates of the children of his brother and sister-in-law in the town's vital records. "John Buttrick Brown" was listed there plain as day...their second child and the birth date matched what I have, via written records that my mom still has: 8-Dec-1790.
The day after I saw these records (in July-2003), my wife and I located the small graveyard in Sebago, where John B. Brown and his wife Betsy Stearns Brown are buried.