The best source of information on the population status of Green Heron is the Breeding Bird Survey (BBS). Although the BBS is a roadside survey, it samples much of the Green Heron's breeding range and trends have high precision, allowing for the results to be considered highly reliable. The national BBS data show modest roughly decadal fluctuations in abundance, but overall a moderate long-term decrease in abundance of 35% since the early 1970s, with the steepest decline occurring in the 1980s. Among regions with at least medium reliability in trends, there has been little change in central parts of Ontario and Quebec, a moderate decrease in southern Ontario and Quebec, and a large decrease in the Maritimes. With the majority of Canadian breeders in Ontario, the Atlas of the Breeding Birds of Ontario provides good coverage of the Green Heron population, although results only cover the 20-year period between the first and second Atlas (early 1980s vs. early 2000s). Atlas results also suggest a moderate decrease in distribution during this time, including significant decreases in the probability of observation in all regions where it nested.

The goal for Green Heron is to increase the population to the level it was at in the early 1970s, based on the Breeding Bird Survey. Trend data show that Green Heron is currently below its goal range and continuing to decline. Despite this, analysis of recent trends and potential growth rates suggests that Green Heron could reach its population goal by 2050, but only if timely conservation action is taken.