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 minimus) [XC781726]
by Ray Cooke from San Bernardino National Wildlife Refuge, Cochise County, Arizona, United States (call)
Least Flycatcher (Empidonax minimus) [XC252000]
by James Rigby from Colima, Cuscatlan, El Salvador (call)
Subspecies
No subspecies.
Probably diverged from other members of genus c. 1·8 million years ago, in late Pliocene or early Pleistocene.