Delaware is a Mid-Atlantic / Southern state located on the East Coast of the United States, and is named for Thomas West, 3rd Baron De La Warr. Population estimates by the Census Bureau for 2005 place the population of Delaware at 843,524, moving from the 45th most populous state at the 2000 Census to the 46th most populous. Despite this, it is the 7th most densely populated state with a population density of 320 more people per square mile than the national average, ranking ahead of states such as Florida, California, and Texas.

Before Delaware was settled by Europeans, the area was home to the Eastern Algonquian tribes known as the Unami Lenape or Delaware throughout the Delaware valley, and the Nanticoke along the rivers leading into the Chesapeake Bay. The Unami Lenape in the Delaware valley were closely related to Munsee Lenape tribes along the Hudson River. They had a settled hunting and agricultural society, and they rapidly became middlemen in an increasingly frantic fur trade with their ancient enemy, the Minqua or Susquehannock. With the loss of their lands on the Delaware River and the destruction of the Minqua by the Iroquois of the Five Nations in the 1670s, the remnants of the Lenape left the region and moved over the Alleghany Mountains by the mid-18th century.

The Dutch were the first Europeans to settle in present-day Delaware by establishing a trading post at Zwaanendael, near the site of Lewes in 1631. Within a year all the settlers were killed in a dispute with Native Americans. In 1638 a Swedish trading post and colony was established at Fort Christina (now in Wilmington) by the Dutchman Peter Minuit at the head of a group of Swedes, Finns and Dutch. Thirteen years later the Dutch, reinvigorated by the leadership of Peter Stuyvesant, established a new fort in 1651 at present-day New Castle, and in 1655 they took over the entire Swedish colony, incorporating it into the Dutch New Netherland.

Only nine years later, in 1664, the Dutch were themselves forcibly removed by a British expedition under the direction of James, the Duke of York. Fighting off a prior claim by Cæcilius Calvert, 2nd Baron Baltimore, Proprietor of Maryland, the Duke passed his somewhat dubious ownership on to William Penn in 1682. Penn strongly desired access to the sea for his Pennsylvania province and leased what then came to be known as the "Lower Counties on the Delaware" from the Duke.

Penn established representative government and briefly combined his two possessions under one General Assembly in 1682. However, by 1704 the Province of Pennsylvania had grown so large that their representatives wanted to make decisions without the assent of the Lower Counties and the two groups of representatives began meeting on their own, one at Philadelphia, and the other at New Castle. Penn and his heirs remained Proprietors of both and always appointed the same person Governor for their Province of Pennsylvania and their territory of the Lower Counties.

Like the other middle colonies, the Lower Counties on the Delaware initially showed little enthusiasm for a break with Britain. The citizenry had a good relationship with the Proprietary government, and generally were allowed more independence of action in their Colonial Assembly than in other colonies. Nevertheless, there was strong objection to the seemingly arbitrary measures of Parliament, and it was well understood that the territory's very existence as a separate entity depended upon its keeping step with its powerful neighbors, especially Pennsylvania.

So it was that New Castle lawyer Thomas McKean denounced the Stamp Act in the strongest terms, and Kent County native John Dickinson, became the "Penman of the Revolution." Anticipating the Declaration of Independence, Patriot leaders Thomas McKean and Caesar Rodney convinced the Colonial Assembly to declare itself separated from British and Pennsylvania rule on June 15, 1776, but the person best representing Delaware's majority, George Read, could not bring himself to vote for a Declaration of Independence. Only the dramatic overnight ride of Caesar Rodney gave the delegation the votes needed to cast Delaware's vote for Independence. Once the Declaration was adopted, however, Read signed the document.

Initially led by John Haslet, Delaware provided one of the premier regiments in the Continental Army, known as the "Delaware Blues" and nicknamed the "Blue Hen Chickens." In August 1777 General Sir William Howe led a British army through Delaware on his way to a victory at the Battle of Brandywine and capture of the city of Philadelphia. The only real engagement on Delaware soil was fought on September 3, 1777, at Cooch's Bridge in New Castle County. It is believed to be the first time that the Stars and Stripes was flown in battle.

Following the Battle of Brandywine, Wilmington was occupied by the British, and State President John McKinly was taken prisoner. The British remained in control of the Delaware River for much of the rest of the war, disrupting commerce and providing encouragement to an active Loyalist portion of the population, particularly in Sussex County. Only the repeated military activities of State President Caesar Rodney were able to control them.

Following the American Revolution, statesmen from Delaware were among the leading proponents of a strong central United States government with equal representation for each state. Once the Connecticut Compromise was reached—creating a U.S. Senate and U.S. House of Representatives—the leaders in Delaware were able to easily secure ratification of the U.S. Constitution on December 7, 1787, making Delaware the first state to do so.

Many colonial settlers came from Maryland and Virginia which had been experiencing a population boom. The economies of these colonies were largely based on tobacco and were increasingly dependent on slave labor. At the end of the colonial period, slavery in Delaware began a precipitous decline. Shifts in the agriculture economy, the efforts of local Methodists and Quakers, and greater governmental regulation were all factors. Attempts to abolish slavery failed by narrow margins. By the 1860 census there were only about 1,800 slaves in a state of 90,000 people, including nearly 20,000 free African Americans. When he freed his slaves in 1777, John Dickinson was Delaware's largest slave owner with 37 slaves. By 1860 the largest owner had 16 slaves.

The oldest black church in the country was chartered in Delaware by former slave Peter Spencer in 1813 as the "Union Church of Africans," which is now the A.U.M.P. Church. The Big August Quarterly began in 1814 and is the oldest such cultural festival in the country.

During the American Civil War, Delaware was a slave state that remained in the Union (Delaware voted not to secede on January 3, 1861). Delaware had been the first state to embrace the Union by ratifying the constitution and would be the last to leave it, according to Delaware's governor at the time. While most Delaware citizens who fought in the war served in the regiments of the state, some served in companies on the Confederate side in Maryland and Virginia Regiments. Delaware is notable for being the only slave state not to assemble Confederate regiments or militia groups on its own.

Two months before the end of the Civil War, however, Delaware voted on February 18, 1865 to reject the 13th Amendment to the United States Constitution. The issue was north-versus-south inside the state, with the strong Quaker anti-slavery presence in the northern parts. The 1000 or so slaveowners in the southern parts were making a political statement. Slavery ended in Delaware only when the Thirteenth Amendment took effect in December of 1865. When the 15th Amendment gave all blacks the right to vote, the legislature in 1873 passed a poll tax (for everyone) designed to minimize the vote of blacks and poor whites. Delaware quickly adopted other Jim Crow legislation and eventually set up a dual school system topped by the black college Delaware State. From the 1870s to the 1950s, Delaware organized its politics, its legal system, its economy, and its culture on the Southern idea of segregation and the legal principal of separate but equal. The segregated school system was integrated in the mid 1950s.