Admitted to the Union on March 15, 1820 as the 23rd state. Prior to statehood, Maine was District of Maine (Massachusetts).
- Maine’s federal census schedules 1790 - 1810 are separate from those of Massachusetts.
- 1790 federal census extant for all counties.
- 1800 federal census extant for all counties except part of York (missing Hiram and Sandford).
- 1810 federal census extant for all counties except half of Oxford is lost.
- 1820 federal census extant for all counties except part of Washington (missing Houlton Plantation and North Limerick).
- 1830 – 1940 federal censuses extant for all counties except for 1890.