London-Middlesex, Windsor-Essex, Sarnia-Lambton and Chatham-Kent are no longer under a heat warning.
The warning lasted all weekend with daytime highs on Sunday estimated to be around 30 C. With the humidity, forecasters say it felt more like 40 C.
Environment Canada ended all heat warnings just after 9pm on Sunday.
Temperatures are expected to cool a little on Monday with highs in the upper 20s C.