The Lower Counties on the Delaware was a semi-autonomous region of the proprietary Province of Pennsylvania in North America. Although not royally sanctioned, Delaware consisted of the three counties on the west bank of the Delaware River Bay.

In the early 17th century, the area was inhabited by Lenape and possibly Assateague Indian tribes. The first European settlers were Swedes, who established the colony of New Sweden at Fort Christina in present-day Wilmington, Delaware, in 1638. The Dutch captured the colony in 1655 and annexed it to New Netherland to the north. England subsequently took control of it from the Dutch in 1664. In 1682, William Penn, the Quaker proprietor of the Province of Pennsylvania to the north, leased the three lower counties on the Delaware River from James, the Duke of York, who went on to become King James II.

The three lower counties on the Delaware River were governed as part of the Province of Pennsylvania from 1682 to 1701, when the lower counties petitioned for and were granted an independent colonial legislature; the two colonies shared the same governor until 1776. The English colonists who settled in Delaware were mainly Quakers. In the first half of the 18th century, New Castle and Philadelphia became the primary ports of entry to the new world for a quarter of a million Protestant immigrants from Ulster, referred to as Scotch-Irish in America and Ulster Scots in Ireland. Delaware had no established religion at this time.

The American Revolutionary War began in April 1775, and on June 15, 1776, the Delaware Assembly voted to break all ties with Great Britain (and, simultaneously, with Pennsylvania), creating the independent State of Delaware. 1774 1770–1780

From the early Dutch settlement in 1631 to the colony's rule by Pennsylvania in 1682, the land that later became the U.S. state of Delaware changed hands many times. Because of this, Delaware became a heterogeneous society made up of individuals who were diverse in country of origin and religion.

The first European exploration of what would become known as the Delaware Valley was made by the Dutch ship Halve Maen under the command of Henry Hudson in 1609. He was searching for what was believed to be a Northwest Passage to Asia. Hudson sailed into what now is the Delaware Bay. He named it the South River, but this would later change after Samuel Argall came across the mouth of the river in 1610, after being blown off course. Argall later renamed this waterway as the river Delaware, after Thomas West, Lord De La Warr, the second governor of Virginia.

Follow-up expeditions by Cornelius May in 1613 and Cornelius Hendrickson in 1614 mapped the shoreline of what would become the colony and state of Delaware for inclusion in the New Netherland colony. Initial Dutch settlement was centered up the Delaware River at Fort Nassau at Big Timber Creek, south of what is now Gloucester City, New Jersey.

Neither the Dutch nor the English showed any early interest in establishing settlement on this land. It was not until 1629 that agents of the Dutch West India Company, Gillis Hossitt and Jacob Jansz, arrived to negotiate with the Native Americans to purchase land for a colony. (The Dutch always purchased land from the Native Americans, rather than take it by force, but the peoples had differing concepts of property and use. The Native Americans often considered the Dutch "payments" to be gifts in keeping with their Native custom, and expected to share use of the common land.) Hossitt and Jansz secured a treaty granting the Dutch a parcel of land running along the shore eight Dutch miles long and half a Dutch mile deep (roughly 29 by just under 2 US miles). This nearly coincided with the length of the coast of modern Sussex and Kent counties in Delaware.

In 1631 the Dutch sent a group of twenty-eight men to build a fort inside Cape Henlopen on Lewes Creek to establish the Zwaanendael Colony. This first colony was intended to take advantage of the large whale population in the bay and to produce whale oil. A cultural misunderstanding with the Native Americans resulted in their killing of these 28 colonists before a year had passed. Today this site is called Swedes' Landing; it is located in Wilmington, Delaware. Carr translated the name of the post from Dutch into English and it has been known since as New Castle.

After William Penn was granted the province of Pennsylvania by King Charles II in 1681, he asked for and later received the lands of Delaware from the Duke of York. Penn had a very hard time governing Delaware because the economy and geology resembled those of the Chesapeake Bay colonies more than that of Pennsylvania. The lowland areas were developed for tobacco plantations and dependent on enslaved Africans and African Americans for labor. Penn attempted to merge the governments of Pennsylvania and the lower counties of Delaware. Representatives from each area clashed strongly and, in 1701 Penn agreed to allow two assemblies to be elected and conduct their separate affairs. Delawareans would meet in New Castle, and Pennsylvanians would gather in Philadelphia.