A coupler lock for attaching to a trailer hitch coupler. The hitch coupler has a socket. The coupler lock includes a locking bar and a plug member for receipt within the socket of the hitch coupler and supported by the locking bar. The coupler lock includes a base structure removably attached to the locking bar. The base structure includes a locking structure actuatable to lockingly retain the base structure attached to the locking bar so as to retain the plug member within the socket of the hitch coupler. The locking structure is positioned above the plug member with the base structure attached to the locking bar and the plug member retained within the socket of the hitch coupler.