For genealogists who like to trace their family movements, the big gap in census records occurs in 1890. That census was almost entirely destroyed by fire.
So, to track a family in Fond du Lac in 1890, there is a great alternative.
The 1890-91 Fond du Lac City Directory, is really a combined directory of the City of Fond du Lac, the Villages in Fond du Lac County, as well as all the rural residents of the county. While this does not include names and ages of family members, it should help to discover whether your family resided in the county, or had moved on.
Many of the "City" Directories, actually include county information.
The 1876, 1890-91, 1897-98, 1901, 1905 and 1913 all include county residents.
There is also a 1904 directory showing all of the rural routes in the county, with the names of persons receiving mail along those routes.
All of these directories listed above are available for research at the Fond du Lac County Historical Society.