The National Park Service (NPS) was notified of the wildfire in the Miller section of the park in Gary.
A satellite picture showed smoke billowing over Lake Michigan.
Officials said it is contained but not before burning 325 acres. The cause of the fire is under investigation.
A vegetation fire also broke out near the Norfolk Southern rail yard at the Port of Indiana Friday, as well as a prescribed burn at Tolleston East, according to NPS.
The Tolleston Dunes Trial and the surrounding area remained closed to recreation Saturday. The trail system in Miller Woods, including the Paul Douglas Trail is also closed due to the wildfire.
For the latest information, visit the Indiana Dunes NPS website and Facebook page.