Forster's Tern is not particularly well monitored by any surveys, but both the Breeding Bird Survey (BBS) and the Great Lakes Marsh Monitoring Program (MMP) offer some insights into trends. The BBS is not ideally suited to detecting colonial waterbirds, and likely samples less than half of the Canadian range, but nonetheless has medium precision in its trends and overall medium reliability. It shows a slight increase from the early 1970s to late 1990s, followed by a somewhat more rapid decline that has continued ever since, with current levels approximately 43% below those in the early 1970s. The MMP is more spatially and temporally restricted, with data only since 1995. It shows greater inter-annual fluctuations but little overall change in abundance. Overall, there is medium confidence that the population has undergone a moderate decrease.

The goal for Forster's Tern 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 Forster's Tern is currently below its goal range and continuing to decline. Despite this, analysis of recent trends and potential growth rates suggests that Forster's Tern could reach its population goal by 2050, but only if timely conservation action is taken.