Notes: Before statehood, Maine was officially part of the state of Massachusetts and was called the District of Maine. Maine was granted statehood on March 15, 1820 as part of the Missouri Compromise. Nine of the sixteen counties had their borders defined while Maine was still part of Massachusetts, and hence are older than the state itself.
The first county to be created was York County, created as York County, Massachusetts by the government of the Massachusetts Bay Colony in 1652 to govern territories it claimed in southern Maine. No new counties have been created since 1860, when Knox County and Sagadahoc County were created.