Bahamas, Belize, Bermuda, Brazil, Canada (B) (P), Cayman Islands, Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Mexico, Puerto Rico, Turks and Caicos Islands, USA (B).
Vagrant to Antigua and Barbuda, Iceland, Ireland, Jamaica, Montserrat, Netherlands, Portugal, Spain, St Vincent and The Grenadines, United Kingdom, Virgin Islands (British), Virgin Islands (U.S.).
British Columbia south to central Californian coast and east to southern Ontario, Great Lakes and northern Indiana; New York (Long I) to North Carolina; Gulf Coast, from Alabama to Tamaulipas, north-eastern Mexico. Winters from southern California to Panama, and from North Carolina to Gulf of Honduras.
 
Population
Estimated population is 120,000 (2010).
Forster's Tern (Sterna forsteri) [XC452967]
by Paul Marvin from South Padre Is, Birding and Nature Center, Cameron County, Texas, United States (flight call)
Forster's Tern (Sterna forsteri) [XC883553]
by id from Blue Goose Trail, Sabine NWR, Cameron Parish, Louisiana, United States (flight call, screech, keer, peent, kew calls)