It was later than that. I would say around 97'-02' when about a dozen or so Milwaukee area high schools started new programs(Arrowhead, Homestead, Cedarburg, Germantown, Kenosha, Wauwatosa, Kettle Morraine, Greendale, Whitefish Bay, etc). I think in another five years Wisconsin will pass Illinois and Pennsylvania.
I remember compiling a similar list to this in the early 90's on a prodigy college message board when I was in high school. Minnesota and Mass. had nearly identical numbers as the top two followed by Michigan and New York and then a huge dropoff. I do remember Conneticut's and Alaska's numbers being higher while Wisconsin, Missouri, Pennsylvania had signficantly lower numbers back then. Illinois numbers look about the same. I do remember an article in Hockey News? a few years back that said Massachusetts hockey youth participation was rapidly declining as kids were going for more popular sports like football and basketball and USA hockey was starting some sort of grassroots campaign there to get the numbers back up. I wonder if that program is working.