My 78yr old Mom puts empty toilet paper rolls, empty kleenex boxes and used kleenex in linen closet. Is this a sign of Dementia?

My Luz did the same thing with her used protective under for awhile. She put them in the clothes hamper of back into the underwear package.
She had confusion with some other things. Like getting a cup to pour the coffee into instead of pouring it onto the counter.
I would get her an evaluation as soon as possible.

I also think, being from her era plus old memories maybe becoming more frequent, the Great Depression has left memories of desperation that are now taking on a new life. A friend's Dad who is developing Dementia now saves napkins and bags - a new behavior. My friend is concerned as she thought it was very unsanitary.

Something is wrong. First have her tested for a UTI to have that ruled out. Then a good physical. Labs especially to see if there are any deficiencies. When nothing is found, then make that appt with a neurologist.

If this is uncharacteristic behavior, at 78 I would take your mom in for a "check-up". She should be accompanied by her medical PoA or preferably a female family member. At this appointment (with her regular physician) have a pre-written note prepared to discretely give to the nurse requesting a cognitive exam and a UTI test. Make sure someone communicates that she's been displaying odd behaviors. Also while there request a Medical Information Release Form and have your mom designate the medical PoA as her representative. This gets around the HIPAA privacy so that the docs can discuss her info with you and you can give them medical input about her. I did this with my MIL. The medical community is more than happy to do this and it spares your LO of embarrassment and prevents resistance/denial. The outcome of this appointment will direct your next steps with your mother. If she is resistant to going to the doctor it is ok to make up a "therapeutic fib" like Medicare now requires an annual exam, or something like that. Good luck, let us know how it goes!

Putting empty paper boxes and rolls in places where they don't belong is not a good sign. I recommend you take her to a neurologist for a cognitive test.

My 82 y.o. Alzheimer's mother washes and puts away disposable plates in her armoire. She collects tissues, napkins, knickknacks, trinkets, etc. and keeps/hides them in various drawers and boxes in her room. It makes her happy having those things, so I leave her be to do what she wants with them.

She's probably either a sign of her times or she's having some mental issues. Have you asked her why she does this?? Unless she is actually using them for something, throw them out...little by little..