This series of National Archives microfilm provides information on US post office locations. Verbal descriptions of locations are included as well as maps. Time period actually covered varies from one location to another. The 683 rolls of microfilm were originally published as  Microfilm M1126, Post Office Department Records of Site Locations, 1837–1955. Thanks to DL , a member of our Tip of the Day group on Facebook, for reminding me of this wonderful series.
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