It is still there. Opened in 1912. Some recent talk of closing it or selling it. On the northern side of Willmar off Hwy 71, just look for signs that say "do not pick up hitchhikers" and your close.
There is a Hilja Johnson on the MN death index.http://people.mnhs.org/dci
for Ottertail County, MN died in 1970.
That is the only one without a date of birth.
And also interesting is there is another state asylum in Fergus Falls, MN (also in Ottertail County). If it is still there back in 1970.
I found some interesting reading.http://portland.indymedia.org/en/2004/08/294697.shtml
"Minnesota is another area where unmarked graves are being replaced with proper names of deceased patients. In 2003, named grave markers were placed on 128 graves in the Oak Knoll Cemetery in Willmar, MN., while tens, if not hundreds more unmarked graves of former residents of the Willmar State Hospital were found on site."
Back in those days it was very easy to get admitted.
I found this listed on the MN Historical Society website.
Record ID 001728051
Index to burials, ca.1912-1976, in the Willmar State Hospital cemetery, compiled by hospital staff from extant records in the facility.http://www.kandiyohi.com/stay/health.htm