The trailhead for Tolleston Dunes is located off of US-12, also known as Dunes Highway. No entry fee is required and the lot is open between 6:00 am and 11:00 pm daily. Neither water nor restrooms are available at the trailhead. Interestingly enough, the park notes how the "lot is also the site of former sand mining activities from before the park" was established in 1966.
1/4 mile to the west of the main trailhead, there is a wheelchair-accessible picnic area and overlook with two tables that are available on a first-come, first-serve basis. This short overlook trail does not access the main hiking loop at any point but does offer a commanding view over the dunefield.
The trail itself is a "lollipop" that begins and ends on the same path from the parking lot. The long loop (mapped here) is about 2.9 miles total, but a cut-off trail in the middle of the loop offers the option to shorten the trek to only 2.1 miles total.
Sources:
https://en.wikipedia.org/wiki/IndianaDunesNationalPark
https://www.nps.gov/indu/planyourvisit/td16.htm
https://www.fs.fed.us/wildflowers/plant-of-the-week/opuntiahumifusa.shtml