According to the United States Census Bureau, the township has a total area of , of which , or 0.12%, are water. It is located in the Delaware watershed. Saucon Creek begins in Lower Milford and drains part of it north into the Lehigh River. Lower Milford is also the source of three tributary creeks of Perkiomen Creek, which drains south to the Schuylkill River: Hosensack Creek (which starts near the source of the Saucon), Unami Creek, and Macoby Creek. The majority of the township is hilly and is located in the South Mountains and on Mill Hill to the south and east of the Hosensack Valley.