kaitoku-I'd asked the same question you've posed on an earlier incarnation of this site. My question was prompted by a postcard on eBay of a trolley car in Shawmut, Maine.
(I'd been searching on "Shawmut" looking for items listed for the Pittsburg & Shawmut and Pittsburg, Shawmut and Northern Railroads.)
Supposedly, Shawmut, ME was the most northeasterly spot in the US with trolley service and it was stated on the postcard that one could ride from that point to Washington, DC via trolley. This elicited a number of responses, and as BaltOhio has already mentioned, there was some question of river crossings in the New York/New Jersey area.
One of the respondents mentioned a book or magazine article written by some adventurous soul who took his bride on a honeymoon trip via trolley covering these lines in the early 1920's IIRC.
Unfortunately this information was "lost in the ether" when the previous version of this site went down.
After my initial reply I decided to try the trusty "Google" search. The book is titled "A Trolley Honeymoon From Delaware to Maine" by Clinton W. Lucas, printed in 1904, about 20 years earlier than I'd initially thought. More information here:
http://www.archive.org/stream/trolleyho ... a_djvu.txt