fishboat

I live south of Milwaukee and know the cycling options from Waukegan, IL to Door County fairly well.

Weather that time of year..shouldn't be an issue as long as you have clothing for cooler weather...overall though, temps would be great for cycling. The biggest issue is a N, NE, or E wind as that'll pull air off the lake, which will be quite cool. Swimming.. swimming in Lake Michigan is very popular all summer. Again, the wind is the key factor. If you have westerly winds then the warmer surface water is pushed east to the Michigan shoreline & the cooler water (50's-60ish) replaces the warm water on the WI shoreline. If the wind is easterly, then the opposite happens. Warm water (70ish+ in the summer) is pushed to the WI shore and people dive in. Shallow bays of Lake Michigan also warm much faster than open water shorelines.

As for your suggested route... I'd do some searching on RWGPS as you find all kinds of routes in the areas you'll be visiting or passing through. There are decent routes from Union Station up to the WI state line. You'd have to keep a close eye on navigation, but it's a well established origin-destination. Once you get to Illinois Beach State Park, it's a great ride to Door County with 85%+ of it on dedicated multi-use trails..nearly all paved with some rail-trail surfaces here and there. I have (RWGPS) routes for the entire way. Not sure if you're interested in roads or MUPs..

If you're not interested in riding up from Chicago, you might consider jumping off the Hiawatha in Sturtevant. There's two campgrounds in Racine county..Cliffside will be the best and just a few miles from the Oak Leaf Trailhead on County Line Road..that trail takes you up to Sheboygan Falls. Touring cyclists are common at Cliffside. I'm not sure about taking a bike off at the Sturevant stop..you'd have to check. Navigating through Milwaukee is easy..if you know the route. Depending on when you're passing through, I may be able to ride you through the Oak Leaf Trailhead to the north side of downtown Milw..from there it's clear sailing to Port Washington and beyond.

As for "2 night stay in WI State Parks.."..that's news to me. I've camped in WI for 40+ years..not heard of the two night thing. WI is one of the states that has a hiker-biker no-turn-away policy. If a state park is full, and you come in under your own power, they'll find a place for you to camp. Only one night is allowed though under this rule.

Once in Door County..stay away from hwys 57 & 42. After that, about anywhere is good riding. RWGPS has lots of routes up there. You can take the Ahnapee State Trail from Kewaunee to Sturgeon Bay. Potowatomi State Park is in Sturgeon Bay and is much nicer than Peninsula, for camping at least. However, Peninsula is a fair bit north and possibly closer to areas you want to be in. Peninsula is a big park, but gets very busy in season. Peninsula State Park hosts a theater group in the summer and has an outdoor theater..very good..not sure how early the performances start.

Lots of options for the trip (routes, day rides, lodging..) depending on what you're interested in.