A Slave in Lancaster County on the Eve of the Civil War?

"Historical Geography" map about Slavery, 1888 (See discussion at Civil War Memory)

While researching Samuel Evans, native of Columbia and Quartermaster of the 5th Pennsylvania Reserves, for his correspondence after the Battle of South Mountain published in the Columbia Spy, I stumbled across a very interesting note in that newspaper. In light of a post by Kevin Levin mentioning slavery in the North, I thought I'd raise the issue here to ask for any research advice.

In the April 11, 1857, Columbia Spy <link>, there’s a note that according to the 1857 Septennial Census one enslaved person still resided in Lancaster County. It explained that anyone who was a slave in 1780 would continue being a slave according to Pennsylvania’s emancipation law, implying that this person was at least 77 years old in 1857.  I have no further information about this person and almost no familiarity with researching these types of records.  However, once I had a name, I bet it wouldn't be terribly difficult to find more pieces to the story. 

Does anyone have any suggestions about where to begin researching?  Or know what the 1857 Septennial Census is?  If so, please post a comment below, or contact me at vince <at> lancasteratwar.com. 

My next step would be to check out Daily Evening Express issues from around April 11, 1857,  to see if J.M.W. Geist had anything to say on this topic, but I don't expect to have that opportunity anytime soon.