When did the colloquial phrase "up north" and "down south" begin to be used? I am trying to find more information for a book I am working on that takes place around 1830 and am not sure if this was in use around that time.
The Corpus of Historical American English includes American texts from 1810, and sorted by decade. Searching for the phrases with "up|down north|south" gives the following results for the 1830s (out of 13,773,987 words):
UP NORTH 3
DOWN SOUTH 13
DOWN NORTH 1
UP SOUTH 0
Incidentally, the one instance of the phrase "down North" in the 1830s comes from this phrase: "the boundary line is uniformly laid down North of the river St. John"; it doesn't really provide a counterexample, as the two words aren't being used together as a phrase.
On the other hand, all instances of "up North" and "down South" from the 1830s are being used as a phrase:
"Some of our folks down South say, if the Bank is put down, we shall all be split up..."
"I was thinking to get' em to go up north a piece."
Other decades in the 19th century give similar results: "down south" and "up north" are much more common than the other two. There are very few instances before the 1830s, but that may be because the size of the subcorpora before the 1830s are much smaller.
So it seems these phrases were at least in use by the 1830s, and possibly earlier.