Eureka is a city in Navarro County, Texas, United States.

The settlement developed around a log schoolhouse known as Dunn's School just before the Civil War.

In 1870, residents applied for a post office, and at a Grange meeting decided on the name Eureka.

By 1885, Eureka reported several steam gristmills and cotton gins, two churches, a district school, and an estimated population of twenty-five.

The City of Eureka is served by the Mildred Independent School District.