- His papers are at the MHS. This is the couple which built Tulip Hill. He and his wife were birthright Friends, and first cousins (a marriage frowned upon by Friends).
See the "Samuel and John Galloway papers, 1739-1812" at the New York Public Library. Collection Description: "Selected correspondence available on microfilm; New York Public Library. Samuel and John Galloway were merchants of Annapolis and Chestertown, Maryland. Collection consists of mercantile and family correspondence, and accounts of Samuel and John Galloway relating to trade in Negro slaves, tobacco, flour, horses, and general merchandise. Also, John Galloway's account book, 1777-1780. Correspondents include Robert Morris, Thomas Ringgold, Edward Tilghman, James Tilghman, and Tench Tilghman." This is clearly the same Samuel (dates are 1720-1785); I assume that John ("fl. 1775-1783") would be his son.
Also see this collection at the Library of Congress: "Galloway-Maxcy-Markoe family papers, 1654-1888 (bulk 1750-1860)." Here is the collection description:
"Correspondence, business papers, financial records, legal documents, speeches, reports, essays, memoranda, and other papers relating to economic conditions in Maryland (1750-1818) and foreign affairs and political events in the 1840's and 1850's. Includes the manuscript of Virgil Maxcy's biography of John C. Calhoun and numerous letters from Calhoun. Other correspondents include members of the Cheston, Chew, Howard, and Tilghman families, Lewis Cass, Daniel Dulany, Peter Force, Alexander Hamilton, Jr., David Hoffman, Francis Scott Key, George McDuffie, John F. Mercer, James Monroe, Joel R. Poinsett, Richard Rush, Joseph Story, Benjamin Tasker, Jr., George Washington, and Daniel Webster. Microfilm edition of the Higginson & Bird letterbook available, no. 16,289. Members of the Galloway, Maxcy (Maxey), and Markoe families represented include Samuel Galloway (1720-1785) and his son, John (d. 1810), merchants; John's son-in-law, Virgil Maxcy (1785-1844), lawyer, politician, and diplomat; and Virgil's son-in-law, Francis Markoe, public official."
There are also the "Cheston-Galloway Papers, 1684-1961" at the Maryland Historical Society.