If you are a Milwaukee County resident, this cryptically named but very useful county web site will tell you which districts you live in. Carefully enter your address piece by piece rather than all on one line, and you will learn your supervisory and alder(manic?) district, as well as your Congressional district, state assembly and senate districts, and finally, city ward. All good things to know at the voting booth.
You can then click on search results to try and find your representative’s information. To get contact information for anyone other than your county board rep will require a little further digging and clicking, but it can be done with a little patience.