Dear David,
John H. Wigger's Taking Heaven by Storm: Methodism and the Rise of Popular Christianity in America (New York: Oxford University Press, 1998) is a good introduction to the itineracy system in the specific context of Methodism, though it should not be
forgotten that clergy of other denominations also itinerated. Elizabeth Elkin Grammer's
Some Wild Visions: Autobiographies by Female Itinerant Evangelists in Nineteenth-Century America (New York: Oxford University Press, 2003) is written from a literary criticism perspective but may still be of interest. As for individual diaries, they're
just about innumerable. Here's a list in rough chronological order just of the most accessible, courtesy of Laura Arksey's excellent subject index in
American Diaries: An Annotated Bibliography of Published American Diaries and Journals--
Isaac Backus (1724-1806), The Diary of Isaac Backus. Ed. William G. McLoughlin. Providence: Brown, 1979.
John Cuthbertson (1719-1791), extracts in William L. Fisk, Jr., "The Diary of John Cuthbertson, Missionary to the covenanters of Colonial Pennsylvania," Pennsylvania Magazine of History and Biography 73 (1949): 441-458.
Charles Woodmason (fl. 1766-68), reproduced in The Carolina Backcountry on the Eve of the Revolution, ed. Richard J. Hooker, pp. 3-66. Chapel Hill: UNC Press, 1953.
Joseph Pilmore (1739-1825), The Journal of Joseph Pilmore, Methodist Itinerant, ed. Frederick E. Maser and Howard T. Maag (Philadelphia: Historical Society of the Philadelphia Annual Conference of the United Methodist Church, 1969).
Francis Asbury (1745-1816), The Journal and Letters of Francis Asbury, ed. Elmer T. Clark (London: Epworth/Nashville: Abingdon, 1958).
Freeborn Garrettson (1752-1827), The Experience and Travels of Mr. Freeborn Garrettson, Minister of the Methodist-Episcopal Church in North America (Philadelphia: printed by Joseph Crukshank, 1791).
Jesse Lee (1758-1816), Memoir of the Rev. Jesse Lee, with Extracts from His Journals, ed. Minton Thrift (New York: N. Bangs and T. Mason for the Methodist Episcopal Church, 1823; reprinted New York: Arno, 1969).
James Meacham (1763-1820), "A Journal and Travel of James Meacham," Duke University Trinity College Historical Papers ser. 9 (1912): 66-95 and ser. 10 (1914): 87-102.
Nathan Perkins (1749-1838), A Narrative of a Tour Through the State of Vermont (Woodstock, Vt.: Elm Tree Press, 1920)
Richard Whatcoat (1736-1806), reproduced in The Methodists: A Collection of Source Materials, ed. William Warren Sweet, pp. 74-122 (Chicago: University of Chicago Press, 1946).
William Hill (fl. 1790-1791), reproduced in The Presbyterians, 1783-1840: A Collection of Source Materials, ed. William Warren Sweet, pp. 755-777 (New York: Harper and Brothers, 1936).
Lorenzo Dow (1777-1834), History of Cosmopolite, or, the Four Volumes of Lorenzo's Journal, Concentrated in One (Philadelphia: Joseph Rakestraw, 1815). Later circulated under the titles Perambulations of Cosmopolite and The Dealings of God, Man, and the Devil.
Benjamin Lakin (1767-1849), reproduced in The Methodists: A Collection of Source Materials, ed. William Warren Sweet, pp. 203-260 (Chicago: University of Chicago Press, 1946).
Joel Winch (fl. 1802-1806), "The Rev. Joel Winch, Pioneer Minister: Selections from His Diaries," ed. Arthur W. Peach, Vermont Historical Society Proceedings 9 (1941): 235-270 and 10 (1942): 21-35, 83-103.
John Early (1786-1873), "Diary of John Early, Bishop of the Methodist Episcopal Church, South," ed. Collins Denny, Virginia Magazine of History and Biography 33 (1925): 166-175, 283-287; 34 (1926): 130-137, 237-251, 299-312; 35 (1927): 7-12, 280-286; 36 (1928):
175-179, 239-248, 328-332; 37 (1929): 130-138, 256-260; 38 (1930): 251-258; 39 (1931): 41-45, 146-151; 40 (1932): 70-74, 147-154 (incomplete).
William Williamson (fl. 1809), "A Missionary Journey in Ohio in 1809," ed. Guy S. Klett, Journal of the Presbyterian Historical Society 27 (1949): 229-234.
William Colbert (fl. 1810), "A Methodist Circuit Rider among the Berks County Dutch," ed. Don Yoder, Pennsylvania Dutchman 2, no. 13 (Dec. 1, 1950): 1, 5-6.
Joseph P. Howe (fl. 1813-1814), "A Journal of Two Missionary Tours Made in Kentucky and Tennessee," ed. Thomas C. Pears, Jr., Presbyterian Historical Society Journal 16 (1935-1936): 373-388.
Thomas Nixon (1793-1872), excerpt in John G. Jones, A Complete History of Methodism as Connected with the Mississippi Conference of the Methodist Episcopal Church, South (Nashville: Southern Methodist Publishing House, 1887), 1:396-397.
John E. Miller (1792-1847), "John Miller's Missionary Journal," ed. Jasper W. Cross, Journal of Presbyterian History 47 (1969): 226-261.
Hemen Bangs (1790-1869), The Autobiography and Journal of the Rev. Hemen Bangs (New York: N. Tibbals and Son, 1872).
Henry Bryson (1799-1874), "Frontier Evangelist: The Journal of Henry Bryson," ed. John R. Williams, Alabama Historical Quarterly 42 (1980): 5-39.
Matthew Simpson (1811-1884), passim in George R. Crooks, The Life of Bishop Matthew Simpson, of the Methodist Episcopal Church (New York: Harper & Brothers, 1890).
James Gilruth (1793-1873), reproduced in The Methodists: A Collection of Source Materials, ed. William Warren Sweet, pp. 370-467 (Chicago: University of Chicago Press, 1946).
Alfred Brunson (1793-1886), "A Methodist Circuit Rider's Horseback Tour from Pennsylvania to Wisconsin," Wisconsin Historical Collections 15 (1900): 264-291.
James-Hanmer Francis (1796-1863), "Diary of the Rev. James-Hanmer Francis," ed. Winifred L. Holman, Ohio State Archeological and Historical Quarterly 51 (1942): 41-61.
Salmon Stebbins (1795-1882), "Journal of Salmon Stebbins," Wisconsin Magazine of History 9 (1925-1926): 188-212.
Re: "Those who were Methodists, did they file reports with the sending body?" Sort of yes and no. Elders' annual reports survive in accessible form mostly by way of the statistics published by each conference, which are probably not what you're after. More
nuanced, narrative reports on the spiritual health of each circuit were supposed to be provided at quarterly conferences, and therefore can sometimes be recovered from quarterly conference records, when those were well-managed and survive; I've seen a few
1810s examples at the Maine State Historical Society, for example. I don't, however, know offhand of anything like that making it into print.
And I'm no kind of Johnny Appleseedist, but the popular press presented him as a Swedenborgian, not a Unitarian in the ordinary sense. No clue what polity or record-keeping looked like in that context.
Happy reading,
E. Fulton.