80% of the US lives in an urban area as of 2010.

Note the definition of urban area though: "To qualify as an urban area, the territory identified according to criteria must encompass at least 2,500 people, at least 1,500 of which reside outside institutional group quarters."

Urban really means not clearly rural. But there are a lot of "urban areas" 10s of miles outside metropolitan areas that people would consider exurban with forests and homes on significant acreage.

To clarify even more, Kansas is listed as having almost 80 Urban Areas in the 2010 census. I think many of the people in this thread would flatly classify those areas as rural.