The Reynolds house (aka "Party Mansion") was the family home for the Reynolds family. It is presumed to be in the Main Line area of suburban Philadelphia (The Gang Finds a Dumpster Baby).
It was originally owned by Barbara Reynolds (Mac Bangs Dennis' Mom), but Dennis inherited it after her death. After Dennis violated the terms of Barbara's will by allowing Frank onto the property, the Lawyer stripped Dennis of the house and gave it to the next available kin; Dee Reynolds. (Dennis and Dee's Mom Is Dead)
Shortly after that, the Gang was forced to give the entire house to the Juarez family, as compensation for destroying their house as part of their "home makeover" of the Juarez house. (The Gang Gets Extreme: Home Makeover Edition) The property taxes were too expensive for the Juarez family, so they were forced to sell it. However, the new owners hired Mr. Juarez as a gardener. (Charlie's Mom Has Cancer)