Lebanon is the city of which the Men of Letters Bunker is located. It is the geographic center of the contiguous United States (lower 48).
In 1958, Larry Ganem is one of the members of the chapter of the Men of Letters in Normal, Illinois. Abaddon massacres the Illinois chapter while trying to obtain the key to the Men of Letters Bunker, which he gives to Henry Winchester for safe keeping.
Henry uses magic to create a portal which takes him to the year 2013, but is unknowingly followed by Abaddon. Henry finds Sam and Dean and they manage to locate Larry Ganem, still alive, in Lebanon, Kansas. He gives them the coordinates to the Bunker but he pleads with Sam to lock the key inside the Bunker to prevent Abaddon gaining access to the knowledge kept there. When Abbadon locates Larry, she possess his wife and kills him, while she takes Sam hostage. In an exchange with Dean for the key, Henry is killed but, not before he is able to shoot her in the head with a devil's trap bullet which locks Abaddon into her meatsuit, allowing Dean to decapitate her and ensuring she is trapped in the body.
In the aftermath, the Winchesters take the key and move into the Bunker, eventually turning it into their home.
Sam and Dean hunt down a banshee that has been causing the residents of a retirement home called Oak Park to kill them selves. The home is 15 minutes from the bunker.