The serial number for LG washing machines is located in the owner's manual and is also found on the machine near the detergent dispenser or the back of the control panel. If it is on the back, it can be found on the left side when viewed from the front.
A front-loading washer usually has the serial number located along the top of the door opening. A good place to look on top-loading machines is in the top corner on the right-hand side of the machine. The actual serial number will follow "S/N" and will start with the letters "WM."