The Asylum is was located on what will now be the Fond du Lac convention center. There may be some records in Oshkosh or Madison. However, as stated before, there may be restrictions. Being a medical facility and the way the HIPA laws are interpreted regarding 'Medical' records, they may not be viewable.
There was a cemetery on the grounds but is now on land owned by a golf course (Rolling Meadows). I don't believe there are any headstones there but there is a marker where the cemetery once was.
I have a photo of the County Poor House and Insane Asylum dated 1901 if you would like a copy. I can be contacted at email@example.com