Abstract: A modular cover plate assembly for mounting an electrical circuit device to an electrical outlet box includes at least one electrical circuit device, a cover plate having at least one opening formed therein, and multiple adapters configured for insertion into the at least one opening. For instance the cover plate has one or two openings formed therein of rectangular or circular shape. The adapters can be inserted into the opening so that the cover plate may be used with a variety of different styles of outlet inserts. For instance, the adapters may include an electrical outlet adapter, a switch adapter, and/or a rocker switch adapter. The modular cover plate assembly can have other features to optimize functionality, including corner fastener channels configured to receive and hold screws in place prior to installation, and an adapter cover that allows the assembly to be converted to a 4 11/16 inch cover plate.