
Spoiler alert: 75% of it is gone. This visit/post is about a decade late. Currently, a cookie cutter subdivision is inhabiting the space and all of the buildings are gone.
I haven't heard of anyone visiting it in recent years. And google maps shows a tantalizing portion of the original track still weaving through the trees. There even appeared to be structures in the woods. So I decided a visit was most certainly in order.
sourceMAR was built in late 1965 and was the site of the second SCCA Trans Am race in the spring of 1966. The first Trans Am was at Sebring in March, 1966. Over the years, MAR has hosted many drag races and road races. St. Louis Region ran its National and Regional races here until 1984 when MAR closed its doors to road racing and St. Louis International Raceway opened its new road course in 1985.
sourceMid-America Raceway, in Wentzville, Missouri, once hosted an AMA road race national in the mid-1960s. The MCRA club racing group ran races there in the 1970s and into the early 1980s.
MAR also hosted the Falstaff 350 Camel GT Challenge July 19th and 20th 1975. Which is cool because Falstaff.






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Comparing the maps, we see what was there over 10 years ago:

And all that's left today:

With the help of this map, I can identify the parts that remain:

So Google maps shows that Turn 5 might still be there, but 6,7,8,9 and 10 are definitely still there. And there are structures.
My trek started at turn 5 and found nothing but rubble and tall weeds. But walking a little further, I found sexy flat racetrack pavement. This is looking up at turn 6:

Further down along the straight section facing turn 3 that runs parallel to the creek is a nice tunnel of trees:

Turn 8 answers the mystery of the structures. There's a very old one room house that was evidently important enough to move once upon a time, but not important enough to stabilize after moving. There are also some of what appear to have been concession stands or vendor booths from the raceway sitting directly on the track, obviously moved from elsewhere.

Between 8 and 9 it gets weird. There's a couple of trailers parked and I got a little uneasy approaching them because it looked like someone (and their kid(s)) was living there. They were vacant but still full of stuff, including loan paperwork.



Turn 9:

The end:

If you're nearby, I recommend a visit to anyone who likes motorsports, history and/or sweaty hikes through bug infested weeds.
I don't recommend a visit to anyone not nearby or interested in those things, because the good stuff is long gone, there's no racetrack signage left anywhere and no structures remain other than an overgrown paved road through the woods.
I wish I visited the site 10 years ago, but it was still a nice adventure.
PS, I didn't realize until just now that I didn't venture down towards turn 3. So it looks like there's a small section that I missed.
more links:
http://www.geocities.ws/pr_mar_racing/mar_2000.html
http://www.na-motorsports.com/Tracks/MO/MidAmerica.html