John Mottrom (died 1655), or Mottram, was one of the first, if not the first, white settler in the Northern Neck region of Virginia between 1635 and 1640.^[1]

Mottrom owned property along or near the Great Wicomico River and the Chickacoan River. He also owned land on or close to Hull, King's, and Chickacoan creeks. Mottrom was probably the first Englishman to settle on the Virginia side of the Potomac River, and his retreat was a refuge for Protestants fleeing Lord Calvert's Catholic Maryland.^[11] His home, Coan Hall, served as the first county seat of Northumberland county. Mottrom was a merchant, owning a shallop with which he traded with Maryland.^[

The area was occupied at the time of English settlement by the Algonquian-speaking historic tribes of the Wicocomico and Chickacoan. The county was created by the Virginia General Assembly in 1648 during a period of rapid population growth and geographic expansion. Settlement began in this area of the Northern Neck around 1635.

Originally known as the Indian district Chickacoan, the area was first referred to as Northumberland in the colonial records in 1644. The following year, John Mottrom served as the first burgess for the territory in the House of Burgesses, which met at the capital of the Virginia Colony at Jamestown.

The colonial court ordered the two tribes to merge and by 1655, assigned them a reservation of 4,400 acres (18 km²) near Dividing Creek, south of the Great Wicomico River.^[3] By the early 1700s, the Wicocomico tribe was greatly reduced, and English colonists took control of their lands. They were believed to be extinct as a tribe as, landless, they disappeared from the historical record. Descendants of the last weroance are working to regain recognition as a tribe, the Wicocomico Indian Nation.^[4]

The size of the county was drastically reduced in 1651 and 1653 when the colonial government organized Lancaster and Westmoreland counties from it.

Of the 172 counties that have ever existed in Virginia's history, Northumberland ended up being an "ancestor" to 116 of these –– more than the current 95 counties (several were lost to other states, such as West Virginia).^[5]