[4] According to the United States Census Bureau, the town has a total area of 1.04 square miles (2.69 km2), all land.

[7] The climate in this area is characterized by hot, humid summers and generally mild to cool winters.

In 1755 the land tract of Thomas Cresap (Jr.) named "Leeds" at the future site of Williamsport would become an important supply depot for the Braddock expedition to capture the French fort Duquesne (at present Pittsburgh).

Supplies were transported to this place both west from Rock Creek (today's Georgetown) and south from Pennsylvania.

[12] Just over two months later Dunbar, the highest-ranking surviving, unwounded officer, would lead the remains of the tattered army through Williamsport to Frederick, Maryland on the retreat to Philadelphia.

[13] The land of present-day Williamsport was previously owned by Otho Holland Williams, a Continental Army officer in the American Revolutionary War, and for whom the town is named.

Cedar Grove, Daniel Donnelly House, Elmwood, Rose Hill, Sprechers Mill House, Springfield Farm, Tammany, and the Williamsport Historic District are listed on the National Register of Historic Places.

[14][15] In 1834, boats using a portion of the newly built Chesapeake and Ohio Canal were able to reach Williamsport from Washington, D.C.

In 1873, the Western Maryland Railway extended its line from Hagerstown to Williamsport, in order to gain access to canal traffic.

Coal from Cumberland area mines was one of the principal commodities transferred from canal barges to rail cars at Williamsport.

[17] In 1863, during the Civil War, the overflowing flooding waters of the river prevented General Robert E. Lee's army, on its retreat from Gettysburg, from crossing and making it safely into Virginia for several days.

with having a full-time economic development employee[23] hundreds of thousands of grant dollars were secured for projects including handicap accessibility for town buildings,[24] reconstruction of sewage pump stations,[25] a possible bike-and-boat rental facility,[26] and the town was approved as a Heart of the Civil War Heritage Area Target Investment Zone.

Interstate 81 is the main highway directly serving Williamsport, passing along the town's southeastern border.