Just wanted to share some thoughts with folks planning to visit Wisconsin Dells in the fall, winter or spring...
After Labor Day, the major properties close their outdoor waterparks for the season. Sometimes they keep a couple slides open on the weekends, but by mid-September -- regardless of the run of warm weather -- you are not going to use an outdoor waterpark. In the spring, they slowly open outdoor areas, but most are not fully ready to go until Memorial Day weekend. (It's just too darn cold anyway...)
Mt. Olympus, Kalahari, Great Wolf, Wilderness and Chula Vista have major indoor waterparks that are open year round. Polynesian has an indoor good for smaller kids. Beware of some resorts claiming indoor waterparks that are really nothing more than a pool and a couple of slides. Mt. Olympus, Knuckleheads and -- in December -- the Kalahari have what I'd call indoor amusement parks.
The jetboats, Ducks and boat tours run thru the fall color season usually, but that's weather dependent. Make sure you have a jacket. (They sometimes open as early as March if we have an early spring.)
Go-Karts, mini-golf and other outdoor attractions are usually open into October on warm days and weekends, and reopen in March or April.
Performance attractions -- Rick Wilcox Magic Show, Broadway Dinner Theater, Comedy Club, etc have fewer shows. Shops are hit and miss in the winter. Most restaurants and bars are open.
Keep in mind that the Dells employs a lot of college and high school kids. They just are not available to lifeguard, wait tables, etc. during the week during the school year.
There is plenty to do in the Dells year round, but it takes a bit more planning in the off season than in the summer.
My best advice is to check on-line first about what you want to do, then call and confirm.