At Broom Tree (Irene, SD, near Sioux Falls)
Ignatian 3 day silent retreats:
- one for women: August 15-18
- one for men: July 11-14
Pacem in Terris retreat hermitages are also in the Cities.
Arc Retreat Center is 50 miles north of the Twin Cities (this is an ecumenical retreat house).
A link to eight Catholic retreat centers in the Chicago area.
A link to multiple retreat houses in the Milwaukee area.
Marywood Franciscan Spirituality Center has directed retreats throughout the summer in the North Woods of Wisconsin.
There are some summer retreats (hiking retreats, iconography, etc.) available at the Franciscan Spirituality Center in LaCrosse.
There are also Catholic retreat houses in Iowa, contact them for information. Not to mention New Mellaray Abbey's guesthouse.
More a conference than a retreat, but Steubenville Youth Conferences are widely known--this summer, the closest one to Winona is in Rochester (Steubenville North).
And this list in not exhaustive!
All these retreat houses are different in approach and expectations, so ask questions or talk to people who know some of the options (I know some of these places but not all). Summer can be a great time to make an extended retreat, so do consider it!