Union Station to St. Joseph: Under 2 hours, costs $17. There aren't that many time options, but it gets you right where you want to go.
Union Station to South Bend, IN: 1.5 hours, more expensive. There are quite a few options for the train ride, but you might have to hang out in South Bend until we can arrange pick ups/drop offs (this is about 40 minutes from St. Joseph)
Here's the link to Amtrak, if this option sounds interesting to you: