Klamath Falls (/ˈklæməθ/ KLAM-əth) is a city in and the county seat of Klamath County, Oregon, United States. The city was originally called Linkville when George Nurse founded the town in 1867. It was named after the Link River, on whose falls the city was sited. The name was changed to Klamath Falls in 1893. The population was 21,813 at the 2020 census. With its suburb Altamont, a census-designated place, the population of the town is more than 40,000. The city is on the southeastern shore of the Upper Klamath Lake, at the foothills of the Cascade Range, and is home to the Oregon Institute of Technology.

Logging was the first major industry of Klamath Falls.

At its founding in 1867, Klamath Falls was named Linkville. The name was changed to Klamath Falls in 1892–93. The name Klamath (/ˈklæməθ/) may be a variation of the descriptive native for "people" (in Chinookan) used by the Indigenous peoples of the Northwest Plateau to refer to the region.

The Klamath and Modoc peoples were the first known inhabitants of the area. The Modocs' homeland is about 20 miles (32 km) south of Klamath Falls, but when they were forced onto a reservation with their adversaries, the Klamath, a rebellion ensued and they hid out in nearby lava beds. This led to the Modoc War of 1872–1873, which was a hugely expensive campaign for the US Cavalry, costing an estimated $500,000, the equivalent of over $8 million in 2000. 17 Indigenous people and 83 Americans were killed.

The Applegate Trail, which passes through the lower Klamath area, was blazed in 1846 from west to east in an attempt to provide a safer route for emigrants on the Oregon Trail. The first non-Indigenous settler is considered to have been Wallace Baldwin, a 19-year-old civilian who drove fifty head of horses in the valley in 1852. In 1867, George Nurse, named the small settlement "Linkville", because of Link River north of Lake Ewauna.

The Klamath Reclamation Project began in 1906 to drain marshland and move water to allow for agriculture. With the building of the main "A" Canal, water was first made available on May 22, 1907. Veterans of World War I and World War II were given homesteading opportunities on the reclaimed land.

During World War II, a Japanese-American internment camp, the Tule Lake War Relocation Center, was located in nearby Newell, California, and a satellite of the Camp White, Oregon, POW camp was located just on the Oregon–California border near the town of Tulelake, California. In May 1945, about 30 miles (48 km) east of Klamath Falls, (near Bly, Oregon) a Japanese Fu-Go balloon bomb killed a woman and five children on a church outing. This is said to be the only Japanese-inflicted casualty on the US mainland during the war.

Timber harvesting through the use of railroad was extensive in Klamath County for the first few decades of the 20th century. With the arrival of the Southern Pacific Transportation Company in 1909, Klamath Falls grew quickly from a few hundred to several thousand. Dozens of lumber mills cut fir and pine lumber, and the industry flourished until the late 1980s when the northern spotted owl and other endangered species were driving forces in changing western forest policy.