I'm looking for a detailed list of all the pieces from JitD and all expansions including exact square dimensions (the rulebooks only say "X rooms, Y corridors"). Is there such a thing? I couldn't find anything here or on BGG. Any help would be greatly appreciated. Thanks.

I'm pretty sure that the last time someone asked, they were referred to a file on BGG, but I couldn't point it out to you.

Failing all else, the official quest editor contains piece counts for the base game and Well of Darkness (the tile palette shows the amount of each remaining while you're editing a map), and I imagine avianfoo's WART tileset contains that total for all Descent boxes (combined), though I didn't specifically check for that when I looked at it before, and it probably doesn't break them down by source. (Note AoD contains only corrupted terrain, RtL contains only outdoor tiles (I think), and ToI contains only double-sided tiles.)

Great! Thanks a lot. The WART tilesets contain all information I needed!