Main site with links to the various plans per county:
http://www.sewrpc.org/SEWRPC/Transportation/JurisdictionalHighwayPlans.htm (http://www.sewrpc.org/SEWRPC/Transportation/JurisdictionalHighwayPlans.htm)
For the Racine County plan, there are some maps showing the territorial roads, plank roads, plus early and then-present day state and county highway systems. Page 143 (or 159/162) has a decently detailed map showing the unbuilt Lake and Racine Loop Freeways.
The 1975 Kenosha County plan has similar maps except the detailed map at the end has been switched with a map for Waukesha County.
The 1972 Walworth County plan shows how the unbuilt US 12 freeway would have extended from it's current terminus north of I-43 to Whitewater. The 1990 plan includes discussion of a northern versus southern bypass of Whitewater and improving the interchange at the southern terminus of the US 12 freeway (apparently not undertaken).