Bounders

We have no record of the Bounders before the beginning of The Lord of the Rings, which starts in the year III 3001, so it's impossible to say exactly when the force was first set up. However, the centuries after the foundation of the Shire were some of its most troubled, with the surrounding lands in a state of constant warfare: those times would have called for a force of Bounders, or some equivalent, more than any others in the Shire's history. On that basis, it seems plausible that the Bounders, or at least their precursors, dated back to the earliest times of the Shire's past.

The word 'bound' isn't often used to mean 'border' in modern English, but it survives in a few phrases such as 'out of bounds' or 'beat the bounds'. Indeed 'beating the bounds' - that is, patrolling the borders - was literally the role of the Bounders of the Shire.