Eau Claire is a borough in Butler County, Pennsylvania, United States.

Eau Claire is located in northern Butler County at 41°8′7″N 79°47′52″W / 41.13528°N 79.79778°W / 41.13528; -79.79778 (41.135335, −79.797914).

According to the United States Census Bureau, Eau Claire has a total area of 1.3 square miles (3.3 km2), all land.

The racial makeup of the borough was 99.44% White, 0.28% African American and 0.28% Asian.

17.8% of all households were made up of individuals, and 6.7% had someone living alone who was 65 years of age or older.