Thanks Ernie! One of the unidentified Illinois there is my uncle, Samuel Huson, 14th Illinois. We have the letter his fellow corporal wrote to his parents- horrible to read, but tells of how this man had just returned from burying Sam on the battlefield. In all the chaos, his marker must have become lost- he's now ' missing' despite that letter, must remain forever unknown. I've frequently wondered if perhaps the 14th Illinois's records wouldn't contain something helpful- he was buried by his regiment, near where he fell in the first wave through the camps.
JPK - If your ancestor was buried in an individual grave, I'm afraid it's probably impossible to locate the spot anymore. But if he was buried with the other members of the regiment killed there, then the site has been marked, and you can locate it pretty easily, as outlined below. Also, it sounds as if he was buried very near their first position, so even if he was not buried in the regimental burial site, he was almost certainly buried very nearby.
Here's a link to the monument to the 14th Illinois, located on their first battle line. Click on "View Picture Here" to see it close-up, along with the text on both sides...
http://shilohbattlefield.org/details.asp?WidePhoto=TN003M051L.jpg
Here's where that monument is located on the battlefield. You can of course zoom in and out to get an overall perspective, and switch to "Earth" view to see the landscape....
https://www.google.com/maps/place/3...71051,-88.3483378,16z/data=!4m2!3m1!1s0x0:0x0
Here's a picture of their burial site, which as you'll see on the next map, is very close to their monument...
http://shilohbattlefield.org/details.asp?WidePhoto=TN003TB04L.jpg
And the map-view of it's location....
https://www.google.com/maps/place/3...83633,-88.3423727,15z/data=!4m2!3m1!1s0x0:0x0
The 14th was in support of General McClernand's first defensive line, roughly paralleling the Main Corinth Road (Confederate Road on the map) near what's known as The Crossroads. An intersection a little to the left of the monument on the map. The fighting in this area was incredibly intense before the Confederates finally overran the line. The 14th was one of the regiments that caught the brunt of the attack after the initial breakthrough, and had to deal with both charging Confederates and retreating Federals from the line directly in front of them. Saying it must have been awful probably doesn't do it justice.
If your ancestor was removed to the national cemetery, here's a map showing where in the cemetery his grave would be located, although it sounds like it's probably an 'Unknown.' The front of the cemetery is to your left, and you'll find the 14th Illinois's section near the lower-right of the map....
http://www.shilohbattlefield.org/cemetery/map.htm
Finally, here's a page where you can view all of the markers in the park for your ancestor's regiment...
http://shilohbattlefield.org/results.asp?varCWUNIT=UIL0014RI&Submit=Submit
I hope this helps and that you get the chance to visit the park someday. It's worth the visit.
Perry