I'm pretty sure this cover is dated 1861 but, its real hard to be sure, no contents. It's what's written on the back but, I don't take that as always the case. Scott #20 & Pair of 18s on cover is still a nice cover, regardless of the date.
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed. (The exact & entire wording of the 2nd Amendment to the U.S. Constitution)