I'm up in Lawrence, so the NE part of Mass, and I don't have any Williamettes, but I have Cascade and Mt. Hood. Both of my plants don't seem to be ready for harvest, with the Mt. Hoods the closest by producing the side arms.
I've read though that hop coens can grow pretty much whenever they want after June, and as CaliBrewin said, you can get two harvests sometimes. Are these first year plants or are they more mature? I woudl think if they're in their 2nd year and beyond, it's very possible that you have hop cones ready to pick.
I think the best way to tell is tolook at their color, and as they start turning slightly yellow at the tip, and are still soft to the touch, they are ready.