www.alphadictionary.com

Here's one I haven't seen brought up- the locals 'round these parts often use your'n for a 2nd person singular possessive adjective (not sure if it's used in plural).

The derivation seems perceptible enough: "your one" would be more logical than yours following the pattern of "this one" and "that one". That is an assumption though.

Seems to manifest as an Appalachian Scots-Irish usage.
Is that regionally accurate?

Interestingly Dictionary.com sez:

Origin:
1350–1400; ME, equiv. to your + -n, as in mine

-wheras yours is described as about 100 years older, a mere eyeblink on that scale...

Your'n is common among "country" folks around here in Middle Tennessee and northern Alabama.

I don't recall hearing it in the Pacific Northwest--certainly not by the natives of that place.

My Baltimore born-and-raised cousins used "your'n" all the time when we were kids. No "his'n," though. I know their mother (my father's sister) was born and raised in South Carolina, but I don't know just where their (step)father was from...

... The derivation seems perceptible enough: "your one" would be more logical than yours following the pattern of "this one" and "that one". That is an assumption though.
...
Origin:
1350–1400; ME, equiv. to your + -n, as in mine
...

I prefer the second derivation above because of the parallel structure it implies:

my -->mine
your--> yourn

Be careful how you use and pronounce it though, as in "What's mine is mine and what's yours is your'n."



Note that this is different from "YORN," a label I've seen used in programming for a routine that asks for a Yes OR No answer from a user in a script.

(Historical note: during the Poor People's March On Washington, some of the locals often referred to Resurection City as Insurrection City and the Reflecting Pool as Lake Huron, pronounced with a silent "H." Those were different times ...)