Johann Heuer appears on the 1850 census in Germantown with his wife, Mary. That's the last time she appears on a census. In 1860, John is still in Germantown with 3 children, no wife. In 1870, John is living with his son, Ferdinand in Grafton and in 1880, John is living with my gggrandmother in Milwaukee.
I've checked Milwaukee death records and couldn't find one on him. I've also checked the cemetery where my gggrandmother is buried and he isn't there either.
I've been to both Ozaukee and Washington Counties, but their records in the courthouses don't go back far enough.