Dear Lilo,
The St. Louis Post Dispatch is a newspaper. Many families publish a death notice in the papers which usually give funeral details and occassionally they list the deceased address, often names of surviving and other deceased family members.
St. Louis Public libray system has majority of the newspapers on microfilm and the library has also created an index of obituaries and burial notices published for many past years.
You can also locate a former address with a city directories which the library also holds. They are similar to telephone books which in former times used to list a persons address and occupation even before they had a telephone, however I do believe one had to pay to have their information listed in the directory so possibility exists that not everyone in the city is included.
As far as your Wilhelm is concerned, didn't notice an obitury index listing for him, though could have been published in another newspaper. An entry into the Post index would have been helpful. Perhaps the people buried in the lot with Wilhelm are relations. Finding their obits might be helpful.
Have you found him on the 1880 census by chance which is published at Familysearch?
Perhaps someone on the list has a subscription to Ancestory.com which has alot of the older St. Louis recorder of deeds civil marriage records indexed, and older city directory circa 1890's as well.
Might be able to locate a marriage record Family search for Wilhelm also. Otherwise I suppose best to start with a city directory and find out where he lived to deduce which Parrish he may have belonged to as St. Louis City is rather large place.
Barbie