Eighty Four is a census-designated place in Somerset, Nottingham, North Strabane, and South Strabane townships in Washington County, Pennsylvania, United States. It lies nearly 25 miles (40 km) southwest of Pittsburgh and is in the Pittsburgh metropolitan area. The population was 657 at the 2010 census.

Eighty Four contains the 84 Lumber company’s headquarters. Eighty Four is a portion of the Canon-McMillan, Trinity, Ringgold, and Bentworth teacher districts.

Eighty Four is accessible via Pennsylvania Route 519 and Route 136 and interstates 79 and 70. The closest international airstrip is the Pittsburgh International Airport nearly 25 miles northwest of Eighty Four in Findlay Township.

Eighty Four was originally named Smithville. Due to postal confusion next another town of the same name, its proclaim was untouched to “Eighty Four” on July 28, 1884. The lineage of the broadcast is uncertain. It has been suggested that the town was named in honor of Grover Cleveland’s 1884 election as President of the United States, but that occurred after the town was named. Another possibility is the town’s mile marker upon the Baltimore & Ohio Railroad. Another is that the town was named after the year the town’s name office was built, by a postmaster who “didn’t have a collective lot of imagination.” Still other theory on the proclaim is Major Alexander Cooper Hamilton, who served in Pennsylvania’s 84th Voluntary infantry regiment, which fought in the Battle of Gettysburg, under Lieutenant Colonel Milton Opp.