[Iterated]

Banks take their cash and bring it to their regional Federal Reserve Bank for counting/cleaning/repair/replacement/etc. So pretty much any time a bill lands in a bank it has a good chance of getting sent back to the Fed.

Since most places you pay cash at take it straight to the bank ASAP for security reasons, most of your cash ends up at a bank. In fact, I'm having a hard time thinking of a business other than maybe a hotdog stand that doesn't take 100% of their cash revenues to the bank.

[JumpCrisscross]

On the other hand, a marked bill is likely to be destroyed at replaced if it makes it to the Fed.

[zachrose]

But WheresGeorge tracks $1 bills, which probably turn over in a business's cash register and get returned to random people as change more often than they go back to the bank.

[zeckalpha]

Do they send the cash to the cash's regional reserve, or to the bank's regional reserve?

[shpiel]

Businesses take cash to local bank branches, which then take the cash to closest Federal Reserve branch. Most large cities have Federal Reserve branches even if they are not heads of the regions.