On the EOS-1 series cameras, the serial number will appear as a multi-digit white sequenced number engraved in the frame around the label on the camera's bottom.
The serial number for any other EOS DSLR is located on the bottom, on the camera base plate. (Usually shown in black type in a silver box.)
Examples
EOS 5D Mark III
EOS Rebel T7
EOS R Mirrorless
The serial number for EOS R series Mirrorless cameras is located on the bottom, on the camera base plate. (Usually shown in black type in a silver box.)
Examples
EOS R5
EOS RP
EOS M Mirrorless
The serial number for EOS M series Mirrorless cameras may be on the back of the camera body, under the LCD or printed on the back of the camera's LCD. (Usually shown in black type in a silver box.)