1794 September 2:
Blue Hill post office opened. (source: Maine Philatelic Society. 1995. The Post Offices of Maine: A Rarity Guide.)
Postmaster: Arthur F. Drinkwater. (source: Maine Register and State Reference Book. 1852.)
1940 May 21 through 1950 August 10:
The circular postmark is approximately 30 mm in diameter. The elliptical cancellation at the right of the postmark is approximately 33 mm tall and is composed of four bars above and four bars below the numeral (only "1" found to date).
Blue Hill post office is still in operation.