I don’t think “den” or “rec room” are as used as they used to be either.
My parents do, they had it built about 10 years back. Very common in England.
You raise a ruckus in the rumpus room. Unless, you’ve done it so much it’s now the [del]wreck[/del] rec room.
Is the term “Greatroom” used any more, or is that back to being the Family Room?
Do people outside of CA still have a Mud Room?
Mission accomplished. 
If you need me I’ll be in the refractory.
My grandparents has a sunroom – a room with two walls that were windows from about waist high to the ceiling.
I grew up in a home that had a ‘maids quarters’ or perhaps ‘servant’s quarters’ on the prints. It was a excellent teenage bedroom.
My room in the house where I grew up actually was a garret. It would have been more fun if we had called it that. 
It was actually pretty spacious. The main problem in the winter was that it was unheated. And the squirrels that lived in the eaves.
I lived in a house that had a sleeping porch and a cold pantry.
There’s a version of the Mediterranean-style houses in San Francisco that has a central patio about six feet across, with windows and a door into it from all around so they all get light from the open sky, which is handy when all the houses are built so close together that if you put in a regular window, all you’d see is the wall of your neighbor’s house. One friend of mine called his the felinary, as they exiled the cat to it when they didn’t want to put it out. Another friend of mine grew pot in hers.
I’ve visited a few farmhouses in Ontario (Canada) that have mud rooms.
In some cases the functions the room provides is antiquated, not just the name:
Re. the parlor, one event that took place there was the “lying in state” of a dead family member before the funeral. That’s the reason why “funeral parlors” have that name–the function was outsourced.
A closet, and not the kind we have now. Going back to Shakespeare’s time, in Hamlet, Ophelia says “as I was sewing in my closet”. She means a private room.
I know a community college that’s on a former military base. One building used to be the officers’ quarters and included a ballroom for events like dances for the officers. It’s now used as a meeting room but is still referred to as the Ballroom which can be confusing to newcomers.
The first house I grew up in had a verandah, and it’s still pretty common for houses in rural Australia to have one, as they’re perfect for shade in a desert location. They’re basically a covered deck that runs along the length of at least one side of a house. A porch is smaller, a deck can be uncovered and stretch out into the yard. I think that’s the distinction.
When I’m rich and have my dream home, I’m going to name each room something antiquated as one of my many nerdy affectations. Current list of potential ideas include: The Atrium. The Archive. The Eyrie. The Stables. The Great Hall. The Scullery. The Undercroft.
My goofy youngest sister referred to her tiny back yard as her veranda, and she would go out there “to verand.” I know this post doesn’t really add to the thread, but I felt compelled to share the insanity that has afflicted my family. 
Carry on!
I recommend that we leave our coats in the vestibule, partake of the comestibles available to us in the larder, and retire to the study to consider the evening’s affairs.
Are outbuildings counted here?
We have a tack room, but it’s attached to the barn. We also have a woodshed.
Indeed, and I’d thought its use was intended to sound southerny. Imagine my surprise, then, while watching House Hunters to find people "ooh"ing over the lanai in the Floridian/Georgian homes they were looking at. But it wasn’t the kind of patio the Golden Girls had, so I finally looked up lanai and found out it’s not at all what Blanche led me to believe, or what those House Hunter twits were cooing over.
oohh–I just thought of another: a Florida room!
I’ve never been in one, but I’ve heard folks talk about 'em.
It’s the American version of the conservatory I mentioned upthread: An enclosed porch with large windows and glass roof (and mosquito screens!)
But I think they only use the term in the eastern parts of the US.
I would LOVE to live in a big old fashioned house with a sleeping porch (screened in, please). I would be up there, my own little hideaway, three seasons of the year.
I used to drive past a big honkin’ old Queen Anne house with a turret, and always wondered what it would be like to live up there, in the turret. Someone told me it was just a little storeroom. But I pictured a round room, totally round, with a stained glass window.