Hymn Collection of John Rylands
At University of Manchester, UK: 60,000 hymns collected for editing "Hymns for the Church Universal," 1885.
Mennonite Historical Library: Hartzler Collection
(3000+ books with a strong emphasis on American nineteenth century hymnody) General description of collection.
Regent University Library: Clark Hymnology Collect
http://www.regent.edu/general/library/services/collections/specialcollections.cfm#CLARK%20HYMNOLOGY%
Brief summary with library contact information.
Sacred Music
Bibliography of library holdings; relevant card catalog numbers; a few links (University of Tennessee-Knoxville)
The Hymnal Attic
Roger Hicks, personal collection: complete catalog; also bibliography of published articles.
The Robert Guy McCutchan Collection of Hymnology
[at Claremont] Brief summary; contact information.