The Wisconsin Department of Justice has recently launched an archive of formal Attorney General opinions. The opinions, in PDF, are available from the first bound volume of opinions in 1912 to the present.
Note that the bound opinion volumes were published between 1912 and 1994. From 1900-1912, opinions were printed in the Biennial report of the Attorney General of the State of Wisconsin. Since 1994, individual opinions have been made available on the DOJ website.
Kudos to Amy Thornton, senior librarian, DOJ Division of Legal Services for making this collection available.