These marriage records were compiled by Liahona Research at the LDS Family History Library in Salt Lake City, UT. "This collection is based on years of research by Jordan R. Dodd and his staff at Liahona Research and was first published as a series of books by Precision Indexing Publishers, a division of American Genealogical Lending Library of Bountiful, Utah. Liahona Research conducted their searches in the world-famous collections of the Family History Library in Salt Lake City and all the marriages in this collection can be found in the myriad of records at that library. The staff at Liahona poured through published books and microfilmed copies of original records to collect these marriages." (from the database description at Ancestry). Ancestry digitized the records in 1997 and provides the database to members on its website.
The collection does not include source citations to the original records, which should exist somewhere at the Family History Center, as that is where the original research was done.
Ancestry's interface permits searching by name, date and keyword. Typing the county in the keyword county will limit the results to that county.