I've been reading Christopher Ward's The War of The Revolution and as our intrepid heroes are advancing backwards from White Plains to the Delaware River there are multiple references to "The Jerseys". A bit of internet research reveals that this is apparently a common term for what we now call New Jersey during the Revolutionary War era.
Not being from that part of the world, my knowledge of that region's history is lacking. I'm curious, what's the origin of the term, when did it fall out of favor, all that good stuff?
New Jersey was originally part of New Netherland. When the English took over the colony from the Dutch for the second and final time in 1674, the king of England, Charles II, split the colony up. The land at the mouth of the Hudson and all points north was renamed New York and granted to the king's brother, the Duke of York (later King James II).
The land west of New York Bay and south of the terminus of the Delaware River was split into two, granted to two lords who had been loyal to the crown during the English Civil War as repayment for their service. The land granted to Lord Philip Cartaret was called East Jersey and the land granted to Lord George Berkeley was called West Jersey.
In the 1680s, there was some re-organization of colonial rule where all three colonies (New York, East Jersey, West Jersey) came under the administration of the "Dominion of New England". This didn't work out well, as there was a rebellion in 1689, and the dominion was re-organized once again. The colony of New Jersey was formed in 1702 as a result, composed of the former East Jersey and West Jersey.
Calling the area "the Jerseys" was a throwback to that earlier time of 1674-1702, when New Jersey was two separate colonies.