The George Thacher Papers contain letters to and from George Thacher, letters to and from his wife, Sarah, his children and descendants, and family friends and relatives. The letters are arranged in eleven folders, and are separated either by subject matter or by the identity of the recipient or writer.

Also included in the collection are three notebooks. Two of these notebooks, labeled respectively "To Mr. Cross No. 2," and "To Mr. Cross, No 3," contain Thacher's own copies of his letters to Nathanial Cross, a defender of the orthodox religious beliefs of that period. In these letters, Thacher defends his Unitarian interpretation of scriptures to the religiously orthodox Cross. These two notebooks are grouped with Cross' letters to Thacher, thus forming a complete dialogue. There is also one letter to Thacher from John Gillespie, which also debates religious matters. These letters and notebooks are contained in Folders 4A and Folder 4B.

The third notebook is labeled "Extracts," and contain Thacher's notes on his readings, particularly Gibbon's History, extracts from scriptures, and a copy of a letter from Thacher to the "Society of Protestant Dissenters."

The letters in Folder 3, all dated 1789, were written by Thacher's constituents during his representation of the District of Maine in Massachusetts at the first Federal Congress. In addition to the many letters requesting Thacher's influence in obtaining governmental appointments, these letters reflect the interests of the farmers and merchants of this Northern District of Massaachusetts. Of particular concern during this period is the proposed tax on salt and molasses, in order to raise revenue for the new federal government. Of more general interest is a letter from Samuel Nason of Sanford to Thacher, discussing, among other things, the amendments to the Constitution then being debated in Congress (the Bill of Rights). Nason urges Thacher's support of an amendment protecting the right of every man to bear arms, against a "foreign foe," and warning against the dangers of a standing army in peacetime as a primary threat to freedom.

The exchange of letters between Thacher and Nathaniel Cross, written in 1817, (Folders 4A and 4B) will be of particular interest to students of religious history and doctrine, and to those studying the history of the Unitarian Church in New England. The letters present and attempt to support through logical argument and interpretation of Scripture, the doctrinal position of the "Socinians," the "Trinitarians," and other dogmas of the orthodox clergy in New England. (Socinianism was a religious movement originating in Italy in the mid-sixteenth century, the precursor of Unitarianism, which denied the divinity of Christ, the depravity of man, and the existence of the trinity of Father, Son and Holy Ghost, and maintained the scriptures should be interpreted through human reason.) George Thacher was influential in forming one of the earliest societies of worship in Maine that departed from orthodox religious doctrine.

Folder 5 contains personal letters to Mrs. Sarah Thacher from friends and relatives. The writers are all women, and the contents of the letters of a domestic nature. They contain hints of domestic life, and health care and medicine in the late 1700s and early 1800s. A group of letters from Mary Scollay to Sarah suggests the restrictive life and frequent loneliness of a single woman living in her parents' home. Letters from George Thacher's schoolboy sons to their father (Folders 1 and 2) give interesting descriptions of the required curriculum of studies of that period.