[3] According to the United States Census Bureau, the CDP has a total area of 3.4 square miles (8.8 km2), all land.

Heron has a continental, quasi-Mediterranean climate (Dsb[broken anchor]) that has more in common with northern Idaho and the Pacific Northwest than the rest of Montana.

It has one of the wettest climates in the state (outside isolated mountain areas), averaging nearly 34 inches (860 mm) of precipitation per year.

Winters are wet and often snowy with occasional rain; summers are mostly dry with sunny, warm days and cool to chilly nights.

Overall, Heron's average annual precipitation cycle is similar to that of the Pacific Northwest in its dry summer and wet winter (with a November maximum, as in Seattle, WA), but somewhat transitional into the typical Montana and Wyoming pattern of a May or June maximum, reflected in Heron's continued relatively high rainfall those months.

The combination of these factors with possible orographic lift results in Heron being one of the wettest locations in Montana, mostly a dry state elsewhere.