Old Zionsville is an unincorporated community in Lehigh County, Pennsylvania, United States. Old Zionsville is located along Pennsylvania Route 29 and Pennsylvania Route 100 2.5 miles (4.0 km) southeast of Macungie. Old Zionsville has a box post office with ZIP code 18068. Surrounding areas use the Zionsville zip code of 18092 or the Emmaus zip code of 18049. 
The Upper Milford Township municipal building is located at 5671 Chestnut Street at the former site of Kings Highway Elementary School and has a Saturday farmers' market. There are two churches of the Lutheran and UCC faiths in the village and two more of the Mennonite and Bible Fellowship faiths within a mile to the east near Zionsville.
Old Zionsville is in the Delaware watershed and straddles the divide between the Lehigh and Schuylkill watersheds. While most of the village is drained via the Perkiomen Creek to the Schuylkill River, the northern tier including the municipal building is drained via Leiberts Creek and the Little Lehigh Creek to the Lehigh River. The line runs east-to-west just north of Ridgeway Drive and Walnut Lane.