Eureka is a town in Lincoln County, Montana, United States, 9 miles (14 km) south of the Canada–US border. The population was 1,380 at the 2020 census.

Eureka was founded in the early 1880s as settlers moved north from Missoula and south from Canada; it was originally known as Deweyville. One of the last areas to be developed in Montana in frontier times, logging was a major draw and source of income for decades. Eureka was once billed as the "Christmas Tree Capital of the World," with evergreens shipped to many urban points for holiday sales.

The Canadian fur-trapper and explorer David Thompson visited the area in the early 19th Century during his searches for a route to the Pacific Ocean. Early explorers, finding Indians there growing a native strain of tobacco, named it the Tobacco Plains. In the late 1970s, Eurekans began a "Tobacco Valley Rendezvous" every year in April to commemorate Thompson's visit.

President Harry S. Truman gave a speech in Eureka on October 1, 1952, as part of a whistle-stop tour in support of Adlai Stevenson's ultimately unsuccessful presidential campaign.

Owens & Hurst Lumber mill closed in 2005.

Eureka is located on the Tobacco River in an area known as the Tobacco Valley in the United States and Tobacco Plains in British Columbia.

It is approximately 66 miles (106 km) from Kalispell. The Tobacco River flows west through the southern part of town.

According to the United States Census Bureau, the town has a total area of 1.01 square miles (2.62 km²), all land.