Loyalsock Creek is a 64-mile-long (103 km)tributary of the West Branch Susquehanna River located chiefly in Sullivan and Lycoming counties in Pennsylvania in the United States. As the crow flies, Lycoming County is about 130 miles (209 km) northwest of Philadelphia and 165 miles (266 km) east-northeast of Pittsburgh.
The name is a corruption of a word in the language of the local indigenous peoples meaning "middle creek" (the original was something like Lawi-sahquick). This refers to Loyalsock Creek's location between Lycoming Creek and Muncy Creek, with the mouths of each about 6 miles (10 km) up- and downstream of the mouth of the Loyalsock. Several important trails used by the local indigenous peoples ran along parts of the Loyalsock or crossed it. Two important villages of the local indigenous peoples were located on its banks, one of which, Ots-ton-wak-in, was the home to Madame Montour and her son Andrew Montour, and later became Montoursville.
Loyalsock Creek is 64.3 miles (103.5 km) long. The source is in western Wyoming County near the Sullivan County line, and its confluence with the West Branch Susquehanna River is at Montoursville. The area surrounding the confluence with the Susquehanna River has been flooded numerous times over the past decade, devastating many local homes and businesses.