Historical evidence suggests that great wildfires burning in the Lake States and Canada can affect atmospheric conditions several hundred miles away (Smith 1950; Wexler 1950). Several ‘dark’ or ‘yellow’ days, as such events are commonly called, have been recorded, often with anecdotal or direct evidence pointing to wildfires as the source (Plummer 1912; Ludlum 1972). One such ‘dark day’ occurred across New England in 1780, a year in which people were technologically unable to confirm the source of such a phenomenon. Here we combine written accounts and fire scar evidence to document wildfire as the likely source of the infamous Dark Day of 1780.