Agent for Lord Baltimore in the Susquehanna Valley
Cresap also traveled at least once to Virginia, for Virginia-based trader Claiborne also traded for furs in the lower Susquehanna area of Chesapeake Bay. Cresap fled from Virginia either because of the Native American raids against white settlers in 1722, or because a dozen or more fellow settlers drove him as he cleared timber to make a dwelling and secure his land claim. As Cresap defended himself, he cleft one of his assailants with a broad-ax.
Upon returning to Maryland, Cresap secured a patent to operate a ferry over the Susquehanna at the head of tide-water from Lord Baltimore. Although Captain John Smith had traveled up the Chesapeake, possibly this far, in 1608, Virginians had ceded this area to Maryland, but Pennsylvania also claimed the area as covered by land grants to William Penn. Cresap had little formal education, but became a land surveyor, and was of great service to Lord Baltimore in extending the western boundary of Maryland from the source of the south branch of the Potomac due north, thus adding at least one third more territory to Maryland.
Cresap came to Conejohela Valley in March 1730, and built a block-house on the banks of the river three and one half miles below today's Wrightsville, near the site of Leber's Mill. That same year, he took out a Maryland patent for several 100 acres (400,000 m2) near the river for "Blue Rock Ferry" at same place. In 1731, Cresap was commissioned a justice of the peace for Baltimore County. While Cresap lived in the lower Susquehanna area, he visited the rich valleys 30 miles (48 km) farther up the right bank of the river, now in Hellam and Lower Windsor Townships. He reported the conditions to Lord Baltimore, who as early as 1721 had contemplated extending the northern boundary of Maryland on the west side of the Susquehanna to the northern limits of the fortieth degree of latitude. (See Maryland–Pennsylvania boundary dispute)
Gradually a few settlers from Maryland moved to the Conojohela Valley. They were aggressive to the Pennsylvanians who settled near them. It was not Lord Baltimore's practice to purchase lands from the Indians; instead the Marylanders drove them away by force. The settlers treated the Indians on the west side of the river with cruelty. However, they had no one capable of holding the ground they had taken either from the Indians nor from the Pennsylvanians, who were determined to prevent Baltimore from gaining a foothold on this disputed area.
Cresap became a notorious figure in the Conejohela Flats area—the lower Susquehanna Valley in the area south of Wright's Ferry—where his actions (and those of his men) as an agent on behalf of Lord Baltimore made him a wanted criminal in Pennsylvania. Cresap and his men several times used force to evict men who had considered themselves legal under Pennsylvania's Colonial Charter, but whom Cresap and Lord Baltimore considered squatters interfering with Maryland's charter. Because of the bloodshed during Cresap's War, King George II issued an edict forcing a settlement of the Maryland-Pennsylvania boundary dispute against the claims by Lord Baltimore. Cresap was held a villain in Pennsylvania, and something of a hero in Maryland, which has municipalities named after him. In 1735, he took out a Maryland patent for a group of islands at Blue Rock Ferry, called the "Isles of Promise." After many attempts to capture Cresap, Pennsylvania Sheriff Samuel Smith and 24 armed men finally captured him on 25 November 1736, as his wife stood by him and fought at his side.
By this time the Cresaps had at least two and perhaps three children, the eldest being about 9 years of age. While Pennsylvanians imprisoned Cresap, his wife and children lived with his cousin Daniel Lowe, who drove one of the German settlers from his home in Grist Valley (Kreutz Creek), near Codorus.