The name Pennant Hills originally applied to the area now known as West Pennant Hills, located in the Hills District. However, when the northern railway line was built it passed through what is now Pennant Hills, so a suburb grew around the station and took on the name. The area around Thompsons Corner was renamed West Pennant Hills. Pennant Hills is hilly and the highest altitude is at Observatory Park on Pennant Hills Road, which once was the site of the old astronomical observatory.