This site has more information on the Church History Library.
The current Church History Library building was completed in 2009. It is a state-of-the-art facility designed to house the records of the Church in a way that will preserve them for future generations for hundreds of years to come. The library provides archival storage and public access for materials that chronicle the history of The Church of Jesus Christ of Latter-day Saints from 1830 to the present day. It has 10 main storage rooms that are kept at 55 degrees Fahrenheit, with 35 percent relative humidity. Two special rooms are kept at -4 degrees Fahrenheit for color motion picture films, photographs, and records of special significance. The building contains 230,000 square feet on five floors.
A time capsule was placed in the building when construction was completed. The items inside provide a snapshot of the Church at that point in history.