How much original native prairie land remains in the US and in Minnesota?

Question

How much original native prairie land remains in the US and in Minnesota?

Answer 1

In Minnesota, only 1% is left of the original 18 million acres of native prairie.

According to the Army Corps of Engineers (2005, second link below), "Before European colonization, prairies covered approximately one-third of the land surface in the contiguous United States. Native prairies presently comprise less than

3 percent of their original acreage in the United States, and remaining patches are small, fragmented, and isolated."  

Total area of United States is 9,372,610 km^2, so that would help to figure it out.