More than 56,000 homes were sold last month, which was more than twice as many as sold in the same month a year earlier.
Home sales hit nearly 70,000 in March, but in the two months since, have fallen by 11 and now seven per cent.
CREA says the average selling price can be misleading because it can be skewed by sales of expensive homes in pricey markets such as Toronto and Vancouver.
But even the HPI rose by more than 24 per cent in May compared to the same time last year, which is the highest increase on record.
The slowdown in some Ontario markets is noteworthy mostly because that province drove a lot of the gains on the way up.
Before the pandemic, a benchmark home in Barrie, Ont., located about 100 kilometres north of Toronto, cost about 57 per cent of what a similar home would cost in downtown Toronto.
But that trend seems to be running out of steam now.
Prices are not exactly cooling in the area.