Index of English Literary Manuscripts. Eds. P.J. Croft, Theodore Hofmann, and John Horden. London: Mansell; New York: Bowker, 1980-1997. Volume I: 1450-1625 (2 parts); Volume 2: 1625-1700 (2 parts). Vol.. 3: 1700-1800 (4 parts). Vol. 4: 1800-1900 (3 parts). A descriptive catalog of extant literary manuscripts of over 200 British and Irish authors who thrived from 1450 through the nineteenth century. 7th floor, PR 83 .I5
Location Register of English Literary Manuscripts and Letters: Eighteenth and Nineteenth Centuries. Ed. Davd C. Sutton. London: British Library, 1995. 2 vols. Reference: PR Z 6611.L7 L625 1995
Ricci, Seymour de. Census of Medieval and Renaissance Manuscripts in the United States and Canada. New York: H.W. Wilson, 1935-1940 (3 vols). Supplement: New York: Bibliographical Society of America, 1962. A finding list of Western manuscripts created before 1600 that are owned by institutions and private collectors, arranged by state, city, institution or collector, with indexes at the back of volume 3. Not intended to be definitive (and many of the manuscripts in private collections have since changed hands), but this is still an important starting point for locating medieval and early modern manuscripts. Available as an ebook from the American Council of Learned Society's (ACLS) ebook collection. UCSD's print set is at SRLF; there is also a set at SDSU's Love Library.
Location Register of 20th-Century English Literary Manuscripts and Letters. Maintained (as funding permits) by the University of Reading Library. The printed edition doesn't have the post-1988 updates that the database does, but may still be useful: Reference Z 6611 .L7 L63 1988 (2 volumes).