You should easily be able to find many circuits available on the net for methods of detection and demodulation of OOK signals, they're extremely basic.
Most common method of demodulation is just a simple detector. Rectifying diode and filter. Filter set to pass bit rate of ON-OFF pulse width. In tech terms, a matched filter provide the minimum bandwidth to reduce noise while still being able the recognize the pulses. A comparitor with some hysterisis at output of filter will re-establish the square wave pulses.