In Maine we don't usually go to the county courthouse to find vital records. In this and other New England states, birth, death and marriage records have been kept by towns and cities since colonial days. Municipal clerks in Maine were sometimes expected to return copies of these records to the state, but only in 1892 did this become standard practice. There is, though, one important set of vital records that may be found at Maine courthouses.
Towns in Massachusetts had been sending copies of marriage records to their county's Court of General Sessions for a century when, in 1786, a law was passed requiring the courts to record these marriages "in a book to be kept for that purpose, and no other." After Maine separated from Massachusetts, a similar law was passed, requiring city, town and plantation clerks to return, "to the clerk of the judicial courts for his county, a transcript of all records of marriages made upon his books, during the year for which he was clerk; and it shall be the duty of the clerk of said courts to record the same in a book, to be kept for that purpose." Many of these books survive, and include records of marriages for which no other evidence exists.
Through the efforts of the Maine Genealogical Society, returns from Cumberland, Lincoln, Oxford, Penobscot, Washington and York Counties have been transcribed and published. (Some early York County returns had been published previously, as had those of Waldo County.) Returns from Androscoggin, Hancock, Kennebec, Knox, Piscataquis and Sagadahoc Counties are also available on microfilm at the Maine State Archives. Franklin County returns have been transcribed here.
Some of these marriage records will also be found at FamilySearch, where they may be viewed online. (Click on the camera icon to view images.) These include: Androscoggin County; Aroostook County; Cumberland County; Kennebec County; Lincoln County (more here); Oxford County (relevant images begin here); and Piscataquis County.