Eureka is an unincorporated community in Luce Township, Spencer County, in the U.S. state of Indiana.
Eureka was laid out in 1858. A post office was established at Eureka in 1872, and remained in operation until it was discontinued in 1921. Tradition has it the community was so named after a pioneer exclaimed "Eureka!" when he came upon the site.
Eureka is located at .
The climate in this area is characterized by hot, humid summers and generally mild to cool winters. According to the Köppen Climate Classification system, Eureka has a humid subtropical climate, abbreviated "Cfa" on climate maps.