ArchiveGrid is a free resource for finding libraries, archives, and primary source material throughout the world.
“ArchiveGrid includes over four million records describing archival materials, bringing together information about historical documents, personal papers, family histories, and more. With over 1,000 different archival institutions represented, ArchiveGrid helps researchers looking for primary source materials held in archives, libraries, museums and historical societies.”
Search by keywords (not ancestor names) with locales, churches, societies an ancestor belonged to, etc (items aren’t categorized by names within collections). Don’t limit searches to a single repository in case the collection was donated by a repository outside the locale to which it pertained.