An Act for the Gradual Abolition of Slavery

An Act for the Gradual Abolition of Slavery, passed by the Fifth Pennsylvania General Assembly on 1 March 1780, prescribed an end for slavery in Pennsylvania. It was the first act abolishing slavery in the course of human history to be adopted by a democracy. The Act prohibited further importation of slaves into the state, required Pennsylvania slaveholders to annually register their slaves (with forfeiture for noncompliance, and manumission for the enslaved), and established that all children born in Pennsylvania were free persons regardless of the condition or race of their parents. Those enslaved in Pennsylvania before the 1780 law came into effect remained enslaved for life. Pennsylvania's "gradual abolition"—rather than Massachusetts's 1783 "instant abolition"—became a model for freeing slaves in other Northern states.
1780 Act.
The 1780 Act prohibited further importation of slaves into Pennsylvania, but it also respected the property rights of Pennsylvania slaveholders by not freeing slaves already held in the state. It changed the legal status of future children born to enslaved Pennsylvania mothers from "slave" to "indentured servant", but required those children to work for the mother's master until age 28. To verify that no additional slaves were imported, the Act created a registry of all slaves in the state. Slaveholders who failed to register their slaves annually, or who did it improperly, lost their slaves to manumission.
The 1780 Act specifically exempted members of the U.S. Congress and their personal slaves. Congress was then the only branch of the federal government under the Articles of Confederation, and met in Philadelphia.
1788 Amendment.
An Amendment, created to explain and to close loopholes in the 1780 Act, was passed in the Pennsylvania legislature on 29 March 1788. The Amendment prohibited a Pennsylvania slaveholder from transporting a pregnant enslaved woman out-of-state so her child would be born enslaved; and from separating husbands from wives, and children from parents. It required a Pennsylvania slaveholder to register within six months the birth of a child to an enslaved mother. It prohibited all Pennsylvanians from participating in, building or equipping ships for, or providing material support to the slave trade.
The 1780 Act had allowed a non-resident slaveholder visiting Pennsylvania to hold slaves in the state for up to six months. But a loophole was soon identified and exploited: if the non-resident slaveholder took his slaves out of Pennsylvania before the 6-month deadline, even for one full day, it would void the residency of his slaves. The 1788 Amendment prohibited this rotation of slaves in and out-of-state to subvert Pennsylvania law.
Washington's dilemma.
The 1780 Act had exempted personal slaves owned by members of Congress. By 1790, when Philadelphia became the temporary national capital for 10 years, there were three branches of the federal government under the US Constitution. There was confusion about whether or not the Pennsylvania law extended to all federal officials; members of Congress (legislative branch) remained exempt, but there was uncertainty regarding whether justices of the US Supreme Court (judicial branch) and the US President and the US Cabinet (executive branch) would also be exempt. Attorney General Edmund Randolph lost his personal slaves to manumission because of his misunderstanding of the state law. He conveyed his advice to President George Washington through the president's secretary, Tobias Lear:
This being the case, the Attorney General conceived, that after six months residence, your slaves would be upon no better footing than his. But he observed, that if, before the expiration of six months, they could, upon any pretense whatever, be carried or sent out of the State, but for a single day, a new era would commence on their return, from whence the six months must be dated for it requires an entire six months for them to claim that right.
Washington argued privately that his presence in Philadelphia was solely a consequence of the city being the temporary national capital, and that he remained a citizen of Virginia and subject to its laws on slavery. Still, he was careful not to spend six continuous months in Pennsylvania, which might be interpreted as establishing legal residency. Litigating the issue might have clarified his legal status and that of other slaveholding federal officials, but it also would have called attention to his slaveholding in the President's House and put him at risk of losing those slaves to manumission. It was thought that he followed Randolph's advice and knowingly and repeatedly violated the state's 1788 Amendment by rotating the enslaved Africans in his presidential household into and out of Pennsylvania. 
There is no record of Washington being challenged. According to Lear, the Pennsylvania Abolition Society seems to have turned a blind eye to the President's actions:
That the Society in this city for the abolition of slavery, had determined to give no advice and take no measures for liberating those Slaves which belonged to the Officers of the general Government or members of Congress. But notwithstanding this, there were not wanting persons who would not only give them (the Slaves) advise , but would use all means to entice them from their masters.
Federal officials.
Other slaveholding officers of the executive and judicial branches faced a similar dilemma. Secretary of State Thomas Jefferson swore that he would eventually free his enslaved cook, James Hemings, if Hemings would agree not take advantage of Pennsylvania's abolition law.
Philadelphia's hostile environment for slaveholders was one of the reasons that the Constitution was written to give Congress exclusive control "over such District... as may... become the seat of the government of the United States".
Aftermath.
Those enslaved in Pennsylvania before its 1780 Act became law continued to be lifelong slaves, unless manumitted. Also, the 1780 Act and its 1788 Amendment did not apply to fugitive slaves from other states or their children. Pennsylvania tried to extend rights to fugitive slaves through an 1826 personal liberty law, but it and the 1788 Amendment were ruled unconstitutional by the US Supreme Court in "Prigg v. Pennsylvania" (1842).
Although slavery steadily declined in Pennsylvania, the state that had initially led the way toward abolition tolerated it for decades after it ended in Massachusetts. The 1840 U.S. Census listed 47,854 (99.87%) of the state's blacks as free, and 64 (0.13%) as slaves.
Other states.
New Jersey's gradual abolition law freed future children at birth, but male children of enslaved women could be held until age twenty-five and females until age twenty-one. Those enslaved before passage of the 1804 law remained enslaved for life. The last vestiges of slavery remained in New Jersey until December 6, 1865, when ratification of the Thirteenth Amendment to the United States Constitution ended slavery in the United States. New Jersey's legislature did not approve the Thirteenth Amendment until February 1866, two months after it had been ratified by three-fourths of the states.