First, I meant to say Easement Over an Easement, not and.
Your description of what's going on here leaves something to be desired.
Let's start with the boat dock. Since you referenced Missouri, I assume this dock is located on a lake or a river. You refer to "owners of [the] boat dock," which implies that these persons own the land on which the dock was built. However, maybe you weren't using the word "owners" in a legally precise way and actually meant that you have some sort of lease or other possessory interest.
I am using "owner" (of a slip or boat dock on a USACE waterway) in a legally precise way. Anyone familiar with that, say because they are "owners" themselves, would know that it refers to owning the slip or dock, which is owned as private personal property. It is located on a USACE waterway, which, of course, is owned by the US.
You say that the easement would allow the "owners" to access USACE property, but you didn't explain why the "owners" need or want to access the USACE property. Was it your intent to say that the dock is located on USACE property?
Yes, of course the dock is on USACE property, a lake or river.
See where I'm going?
My best guess is that you meant that the dock is located on USACE property and that the "owners" have a lease with the USACE. In order to get to the dock from "the [c]ounty road" to the dock, one must cross over property owned by the county. Is that about right?
About. As stated, the new policy is that the USACE property can be accessed via a public road when the road abuts the GFTL, so, no need to cross over property owned by the County after that..
&, no need to cross over any private property, which is the new part, not having to own waterfront property in order to have a boat dock.
Now let's look at your question:
Here, you're saying that the "public [c]ounty road" "exists via right-of-way easement." What does that mean? It seems to imply that the road is located on property not owned by the county but over which the county has an easement for the purposes of maintaining the road. However, if that were the case, then it would seem inconsistent with my guess above.
Really? How are roads wherever you are if they don't have right-of-ways? We have a Road and Bridge Commission in our County, and ordinances that prescribe roads. When a subdivision is built, for instance, they currently have to have 50-foot right-of-ways.
For the best shot at good answers, you should (1) clarify the situation, and (2) explain what your interest in the matter is.
With all that said, in the abstract, a county can grant (not "place") an easement over property that it owns.
By the way, using acronyms that aren't part of everyone's everyday vocabulary without explaining what those acronyms stand for isn't generally a good idea. I googled USACE and assume you're referring to the United States Army Corps of Engineers, but I didn't google the other acronym used in your post #7 and haven't the slightest idea what it might mean.
Yes, USACE is common parlance for US Army Corps of Engineers. GFTL may not be as common, but it is Government Fee Take Line, which is the boundary around USACE property that separates it from private property, or, in this example, public property (County Road), but that is not very common since very few roads end at/abut the GFTL.