American Dad! centers on the domestic life of its nominal title character, Stan Smith, a staunchly conservative Republican CIA agent and self-proclaimed patriot. He is married to Francine Smith, a ditzy housewife who is trying to make up for a wild youth. Their two children are Hayley, a passionately liberal college-aged activist, and Steve, a nerdy, wimpy high schooler who constantly attempts to live up to Stan's expectations. The Smith family is also in possession of two bizarre nonhumans — Roger, an escaped alien from Area 51 whom Stan is covertly housing in defiance of his employer, and Klaus, an anthropomorphic goldfish whom the CIA implanted with the brain of an East German Olympic ski jumper.

The Smith Family resides on 43 Cherry Street in the fictional community of Langley Falls, Virginia in the Washington, D.C. metropolitan area. The town name is a composite of Langley and Great Falls, two unincorporated communities located in Fairfax County.

Plots generally center on the misadventures of various family members in their respective realms. Recurring themes include Stan's desire to see Steve mature properly, Roger's desires to establish a life outside of the house, Francine's desire of breaking out of an overly structured lifestyle, Hayley's desire to rebel against her father's politics and Steve's desire to finally become one of the cool kids and "get some boob." Stan's conservatism is treated as buffoonish and self-abnegating on its face.