From the Wisconsin Department of Public Instruction Website: Intro to FAQ About County Library Funding to Libraries in Adjacent Counties (Act 420)
In April, 2006 the legislature passed Senate Bill 272, which was signed into law as 2005 Act 420 by Governor Jim Doyle on May 19, 2006. A new provision of the law extends to adjacent counties the requirement that counties reimburse public libraries for the cost of serving county residents who live in areas of the county without public library service. Beginning in 2008, libraries in adjacent counties, both within and across system borders (but excluding Milwaukee County), may be reimbursed for library use by residents of each of those counties who do not maintain a public library.
As Tony Driessen might say after looking at the above column graph, "Let's 'drill down' to the local level." (The right-hand column is the total amount each library received from adjacent county payments in 2011.)