I discovered this site and topic while researching the Washington, DC trolley route(s) my fiancé Bev used (as a kid) to travel from her home in upper NW Wahington to Glen Echo Park (which is along the Potomac River palisades just west of the DC/MD border). The DC trolley lines from long ago disappeared in 1962 by Congressional mandate and agreement with O. Roy Chalk, who bought the lines after a mishandled strike situation in the 1950s.
Bev's interest and passion, and now mine, are the antique carousels whose heydays coincided with those of the trolley parks, of which Glen Echo was one example. Glen Echo is no longer a full-fledged amusement park, as its only ride is, I believe, the fully restored 1921 Dentzel carousel with its magnificent military band organ. This carousel is the only one owned by the US Government. The park, itself, is vibrant and alive--there are dances, activities for children, arts events, etc.
However, most trolley parks (including the one in Atlanta, GA when I was a kid--Lakewood Park--had carousels and there is a very active organization regarding those rides, the National Carousel Association (NCA). It's website is http://nca-usa.org/
The NCA website has much useful info tailored, of course, to carousel interests. However, there is a census of the roughly 150 remaining operating carousels in North America and many of them are at what used to be trolley parks. You can search by state or other characteristics or produce the entire list. This could help those of you who are trying to pinpoint some details of the old trolley parks.
One park I didn't see mentioned in this forum is Cedar Point in Sandusky, OH, which is a large and active park. I am not sure, but I think this may also have been a trolley park. Cedar Point claims to have more roller coasters than any park in the world, but, from my own viewpoint, they have three
I hope this is of interest.