The parcel, known as the Priory campus, is about 7.6 acres, reports the Wednesday Journal of Oak Park.
The school is unsure of how it will use the property, but officials said it might be used for administrative or athletic offices, spiritual retreats or arts and music programs.
The high school also expects to close next year on the purchase of the athletic fields surrounding the newly acquired property. Fenwick had long leased those fields, which equate to about 11 acres of land, from the Dominican Province of St. Albert the Great.