The River Churn rises at Seven Springs near Cheltenham, Gloucestershire, England and flows south across the Cotswold dip slope passing through Cirencester and joining the River Thames near Cricklade in Wiltshire. Its distance from source to confluence with the Thames is considerably longer than the Thames itself from source to confluence, but historically the Churn is a regarded as a tributary.

The name Churn is ancient, certainly pre-Roman, and probably has its origins in the Celtic language spoken by the Dobunni tribe who controlled the area before the Roman conquest in the 1st Century CE. The original name may have sounded similar to Korinn.

Cognate names and name elements from the area are Cerney, Ciren and Corin as found in the villages of North Cerney , South Cerney , and Cerney Wick , modern Cirencester, and the Roman town name Corinium. All these places are on or close to the River Churn.