The colonial histories of Pennsylvania and Delaware were throughout so closely connected as to necessitate their treatment in connection with each other. Delaware was the first of these two colonies to be the seat of white settlements. This colony, like New Jersey, was first settled by the Swedes, who were conquered by the Dutch, and with the conquest of the latter in 1664, Delaware passed under English rule. The territory included within the area of the present State of Delaware was for a while claimed by Maryland; that colony, however, failed in its efforts to secure possession of this region, which remained under the rule of the Duke of York until 1682, when it was granted to William Penn, who desired an outlet to the sea for his larger colony of Pennsylvania.

William Penn had been one of the Quaker purchasers of New Jersey, and in 1681 secured a grant from Charles I, of a tract of 45,000 square miles, to be held in fealty on an annual payment of two beaver skins. The consideration for the grant was the cancellation of a debt of about 16,000 which had been due from the crown to the father of William Penn.

Both Pennsylvania and Delaware were throughout the whole colonial period charter colonies. The early government established by Penn was extremely just and liberal, and emigration to these colonies was rapid. Pennsylvania has the honor of being the first Christian community in the world which allowed complete religious freedom.

Delaware was first governed as a part of Pennsylvania, and went by the name of "The Territories" or "Three Lower Counties on the Delaware." Later Pennsylvania and Delaware were given separate legislatures, but still continued under the rule of a single governor. The joint governor was appointed by the Proprietors, but the members of the legislature were elected by the people. The governors appointed by the successors of William Penn were so unpopular that after the Declaration of Independence the State Constitutions adopted in these two states provided for an executive council instead of a single executive head. Pennsylvania had only a single branch in her legislative body until 1790. A peculiar feature of the government of Pennsylvania was her council of censors, resembling somewhat in their duties the old Roman officials bearing that title, who assembled once in seven years to report as to whether the State has been well governed during the period since the last meeting of this council. It was this peculiar institution which prevented the threatened civil war between Pennsylvania and Connecticut in 1784.