Morristown National Park contains Jockey Hollow, correct. Parts of it are actually in Somerset County, a long-time park ranger lived on property in the park in Bernardsville on Jockey Hollow Rd...name is Ed Carroll, father of Pete, now coach at Swarthmore, very good runner at Bernards HS in his day. Its Somerset County until you hit the Passaic River. Most people don't run much on the trails on the side of the park, though.
Not much of the Columbia Trail is in Morris County, but some is through Long Valley and towards Flanders.
Either way, many good spots to run up around here. Monmouth County is good, too. I think what the dude was saying about Holmdel is that is boring for just a regular run. Great for x-c workouts, but you have to use your imagination a bit to do a regular 10-12 miler or longer run. Running 3 loops of the 5k course there gets boring, and seems harder than it should...4 gets real tough.
There are more affordable towns in Somerset and Morris County, too, just not Bernardsville or the rest of the Somerset Hills area.
Grote
Grote