- A city, the county seat of Humboldt County, in northern California.
- A city, the county seat of Woodford County, Illinois.
- A city, the county seat of Greenwood County, Kansas.
- A city in Missouri.
- A town in Montana.
- A census-designated place, the county seat of Eureka County, Nevada.
- A town in North Carolina.
- A community in Nova Scotia, Canada
- A research base in Nunavut
- A city in South Dakota.
- A city in Texas.
- A city in Utah.
- A town in Wisconsin.
- A given name, like for the protagonists of Eureka's Castle or Eureka Seven.