Vital records are one of the best resources for genealogists. You will be most successful with your research if you do the search for vital records in the reverse order of life's events. (search for death before marriage, marriage before birth). If you have a child's birthdate, you can begin to narrow down the marriage date.
Vital records in Wisconsin are are maintained by the State and/or County level. You can obtain these records from County Register of Deed Office or the Wisconsin State Vital Records office. The Wisconsin Historical Society, a Family History Center, some local libraries or the county library have indexes for these certificates.
One of the most important things to keep in mind about the information on the vital record is the informant. Sometimes the informant was guessing at the information when asked. Birth dates, parents names, dates of immigration could be wrong or slightly off depending on he knowledge of the informant.