Here are some Church History reference sources IN the library. These are only some examples - there are more! (Remember - these are all found in the REFERENCE section.)
The Modern Catholic Encyclopedia by 
Augustine through the Ages by 
Historical Atlas of Christianity by 
Encyclopedia of Early Christianity by 
The New Cambridge Medieval History, C. 1198-C. 1300 by 
Dictionary of Christianity in America by There are also many reference resources online. Here are some standard Church History sources to know and use.
Pocket Dictionary of Church History by 