Darby and the Underground Railroad
The term "Underground Railroad" generally refers to the various, mostly informal, networks of people who helped freedom seekers escaping slavery during the early 19th century.  Although there was a fugitive slave law as early as 1793, it was the Fugitive Slave Law of 1850, and its harsh penalties for helping freedom seekers, that gave Underground Railroad activity its clandestine flavor, and perhaps helps to explain the scarcity of documentation. Much of what we know comes to us from stories passed down from generation to generation and from oral tradition. There is continuing interest in primary sources including letters, and William Still's classic "The Underground Railroad" published in 1872, is a treasure trove of information. Research continues. 
William Still, author of the classic book The Underground Railroad, worked with Garrett and others as part of the Philadelphia Vigilence Committee. He is buried in Eden Cemetery near Darby
Thomas Garrett of Wilmington Delaware, who along with his brother Edward of Upper Darby, helped some 2,700 people to freedom. Arrested because of his activity, and bankrupted by the Court he nevertheless said "Thou has left me without a dollar...I say to thee and to all in this court room, that if anyone knows a fugitive that wants shelter, send hm to Thomas Garrett and he will befrend him."
Charles Lloyd, proprietor of the Blue Bell Inn on Cobbs Creek who was said to have taken in an escaped slave who appeared in Darby, nursed him back to health and then paid for his passage out of the country
Anti-slavery sentiment in Darby goes back at least as far at 1715 when John Blunston, Caleb Pusey, Nicholas Fairlamb and John Wright laid a concern before the Quarterly Meeting regarding the practice of "importing, buying or selling negroe slaves". (text)
During a recent talk, Nancy Webster said that the Underground Railroad was similar in some ways to the recent sanctuary movement, where someone would be told to collect an individual at a certain place, and then bring them to another place where someone else would take the person on from there and that was all thy knew. The compartmentalization helped to ensure that no-one could betray the network.
The Darby area's involvement with helping freedom-seekers may go back as far as 1787 and the end of George Washington's Presidency when Hercules, his cook, dissappeared "somewhere between Philadelphia and Chester, on the final trip back to Mt. Vernon" (Lawlor). He was never recaptured and it is possible he had local help.  John Jackson of Darby (now Sharon Hill) is known to have aided fugitives and research is continuing.
The Fugitive Slave Law of 1850 made it a crime to harbor, rescue  or conceal a fugitive and provided "in no trial or hearing under this act shall the testimony of such alleged fugitive be admitted in evidence" (R.C. Smedley, History of the Underground Railroad, Pg, 384 (2005 Edition).   
I am indebted to historian Nancy Webster for much information about the Underground Railroad including the context. People create famililiar patterns so that any change in that pattern is noticed. Thus a church was not a good place to hide fugitives because, except for Sunday, there is little activity and people would be noticed. Fugitives might be hidden in a barn or in the woods and moved by people who would be expected to be out at odd hours, such as a farmer making deliveries of milk, or a midwife. Stories of codes and disguises are common, and songs like "Follow the Drinking Gourd", "Wade in the Water", and "Children How Shall I Send Thee" are believed to have UGRR roots.
  .