In 1659, Virginia passed a law requiring every Quaker in the colony either to convert to Anglicanism or to leave. The Quakers of Accomack County, on the southern tip of the Delmarva Peninsula, looked north. They petitioned Charles Calvert, the third Lord Baltimore, in 1661 to settle on the Maryland side of the line. Calvert saw an advantage: the more settlers loyal to him, the harder for Virginia to claim the peninsula. The Quakers landed on the south bank of the Annemessex River in November 1662. A separate group of Anglican Virginians settled to the north along the Manokin. Both groups got land, both got distance from the Virginia Anglican establishment, and Calvert got a frontier of loyal subjects. The county was officially established by proclamation on August 22, 1666 - the eighth in the Province of Maryland. It was named for Mary, Lady Somerset, sister-in-law of Calvert's father. The new county's first hundreds - the colonial subdivisions used for tax and militia organization - were laid out the following January.

The Quakers were not alone for long. In the 1670s, Scottish and Irish Presbyterians began arriving, some from Virginia, some directly from the British Isles. In December 1680, an Anglican settler named William Stevens, who lived in the Rehoboth settlement, wrote to the Presbytery of Laggan in northern Ireland and asked them to send a minister. The Reverend Francis Makemie arrived in 1683. More Irish Presbyterian ministers followed, and the small Pocomoke River towns of Rehoboth and Snow Hill became the center of organized Presbyterianism in colonial America. Makemie's work in Somerset County led directly to the organization of the first Presbytery in Philadelphia in 1706 - the formal beginning of American Presbyterianism. A denomination that would shape education, abolition, and Westward expansion took its first organized breath in a damp Eastern Shore swamp.

In July 1815, after Waterloo, Napoleon Bonaparte tried to escape to the United States. He failed; the British caught him and shipped him to Saint Helena in the South Atlantic. But the conspiracies continued. According to local legend recorded by Hulbert Footner in his 1944 book Rivers of the Eastern Shore, the former mayor of New Orleans, Nicholas Girod, plotted in 1821 to rescue Napoleon from Saint Helena. The plan was to hide him at Beverly House in Princess Anne, the seat of Somerset County, before moving him to the still-extant Napoleon House in New Orleans. The connection ran through Elizabeth Patterson of Baltimore, who had married Napoleon's brother Jerome in 1803, and through her marriage to the gentry of the Lower Eastern Shore - including the King family at Beverly. Napoleon died on Saint Helena on May 5, 1821, before the plot could be tested. The Beverly House still stands in Princess Anne, a brick Georgian mansion that almost held the emperor of France.

For more than a century, Somerset County was a tobacco economy run on enslaved African labor. The crop exhausted the soil, and by the early 1800s some planters had switched to mixed farming. But the Eastern Shore stayed deeply rural and deeply tied to the institution of slavery. While other parts of Maryland saw a growing free Black population - by the Civil War, more than half of all Black Marylanders were free - Somerset County remained dominated by plantation labor. The 2020 census recorded a population of 24,620, the second-smallest of any Maryland county, and 38.6 percent of residents identify as Black or African American - one of the highest proportions in the state, a demographic shadow of the labor system that built the county. The shape of the place is a shape of who was forced to clear it.

Almost half of Somerset County is water. Of its 610 square miles, only 320 are land; the other 291 are tidal Chesapeake. The Deal Island Wildlife Management Area covers 13,000 acres of marsh in the northwest quadrant, with nine miles of flat trails through habitat for waterfowl, muskrats, and bald eagles. Smith Island sits in the middle of the Bay, accessible only by boat from Crisfield - the city at the southern end of the county that calls itself the Crab Capital of the World. Smith Islanders still speak with an accent that popular myth calls Elizabethan but linguists identify as something more original - a dialect that evolved in isolation and bears similarities to West Country English rather than being a direct relic of seventeenth-century speech, the inheritance of a community cut off by water for nearly four centuries. The state cake of Maryland, the eight- to ten-layer Smith Island Cake, comes from here. Somerset County is two things at once: the place where Presbyterianism organized itself in America, and the place where a few hundred fishermen on an eroding island still talk like Cromwell.