Fan - there really isn't a cross county course in Mill Creek Park and I am not sure there is room for one. Cross Country is run on grass - perhaps cross a paved path or two, but its not a road race. Many cross country races take place on golf courses.
Mill Creek would be great for a road race, but unless someone wants to make a course up through some of the golf courses, I don't recall any other place in the park with enough open areas.
Boardman is one of the better courses in the state and the people there really know how to run a race. Lots of parking as well.