Bahamas, Belize, Canada (P), Cayman Islands, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, St Pierre and Miquelon (P), Turks and Caicos Islands, USA (B).
Vagrant to Jamaica.
Central Canada (southern Yukon and north-western interior east to southern Quebec and southern Maritime Provinces) southern in USA to north-eastern Colorado, northern Great Plains, New England and (in Appalachians) north-western Georgia. Winters both slopes of Mexico (southern from Sonora and Tamaulipas), rarely southern USA, south through Central America, at least casually to Costa Rica and central Panama.
 
Population
Estimated population is 14,000,000 (2010).
Least Flycatcher (Empidonax) [XC189968]
by Matt Wistrand from Beatton Provincial Park, British Columbia, Canada (song, song at dawn)
Least Flycatcher (Empidonax minimus) [XC524546]
by Besan\u00e7on from Saint-Bruno-de-Montarville, La Vall\u00e9e-du-Richelieu, Qu\u00e9bec, Canada (call, song)
Subspecies
No subspecies.
Probably diverged from other members of genus c. 1·8 million years ago, in late Pliocene or early Pleistocene.