South Dakota DOT Interactive Map

[M86]

I just found this on South Dakota's DOT website.

http://arcgis.sd.gov/Server/DOT/DOTViewer/

It has every street, road, trail, etc in the state. 

The map can break it down to local jurisdictions, functional classifications, federal aid eligible map, surface types, crash data (since 2010), and imagery.

Click on the left side which category you want to view, and zoom in... a lot.

[SD Mapman]

Oh, they updated it. Now it's actually cool.
To be absurdly nitpicky, there are some minor errors in Lawrence County, but you can't win them all.