1806 September 18:
Unity post office opened. (source: Maine Philatelic Society. 1995. The Post Offices of Maine: A Rarity Guide)
1938 December 20:
The circular postmark is approximately 22 mm in diameter.
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1949 October 4 through 1949 December 5:
The circular postmark is 33–34 mm in diameter. The outer vertical length of the four bars to the right of the circle is 19 mm.
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1950 December 4:
The circular postmark is approximately 30 mm in diameter.
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2020:
Unity post office. 4 Clifford Commons; Unity, Maine 04988. Lat./Long.: N 44°36′20″ x W 69°19′15″
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