In EU4 you can't take a territory without occupying it.
That statement has not been straightforwardly true for
years. (It's so long since they changed it that I can't remember what version it was in.)
You need to occupy a fortified province that is land-connected to the province you want, but you only have to occupy the exact province you want if it belongs to someone other than the country you're signing a peace deal with or there are no other forts land-connected to the province you want.
One of my standard gambits when playing France was to demand Meath/The Pale from England, which would then give me a staging post in these islands.