Here is a link to a story about an upcoming episode of GH which was just filmed at the Union County Court House in Elizabeth, New Jersey, March 12-13 (just before Monster Mania Con).  They say Tango's father recommended the place.

http://www.nj.com/news/local/index.ssf/2009/03/tv_ghost_hunters_searching_for.html

Apparently the producer has high hopes for the episode:

"The crumbling cemetery outside and high-arched rotunda make the site ideal for atmospheric filming, said the show's producer, Jim Dugan.

'Visually, I know I can't lose here', Dugan said. 'I think it's going to play very well.'"

Yes, the Mt. Holly jail is ilocated in an odd place and you are right about getting lost in Mt. Holly at rush hour.  Funny thing is that every time I show up for jury duty at least one person says they actually went over to that building thinking that was where they were supposed to show up.  Thank goodness I've never been involved in any trial in Mt. Holly.