Any advice as to the easiest way to get to St. Mihiel Cemetery from Paris?
Take the train from Paris to Reims - you might have to change - then on to Saint Mihiel.
Unfortunately there doesn't appear to be any bus service nearby (despite the reputation of the country in the USA, French rural public transport can be pretty dire in areas that aren't heavily touristed). The cemetery website suggests that the nearest station is Toul, but from Google Maps it looks as though the nearest is Pont a Mousson, which is served by local trains from Nancy. If you don't have your own car, I would suggest getting a cab from Pont a Mousson or Nancy - the nearest town to the cemetary is Thiaucourt (pronounced TEE-oh-coour).
There is an American military cemetery, Suresnes, at the western edge of Paris with World War I and WWII dead if you cannot work out St. Mihiel. Go to www.abmc.gov to get a list of American military cemeteries in France and all of Europe. If you are not an American, I'm sure you can discover military cemeteries maintained in and by other European countries.
I second the suggestion to see the US military cemetery at Suresnes. One half consists of graves from WW1 and the other half those from WW2. Getting out to WW1 cemeteries in France by public transport can be difficult. I've made it a point to see British, Canadian, German, and French world war one cemeteries in France, some by public transport, for others I was driven.
Because it is so out of the way, I would assume that Jenawirt intends to visit the St. Mihiel cemetery for a specific reason. Perhaps a relative is interred there? If that is the case, it is not very helpful to give suggestions for alternatives American cemeterys.
The big US WW1 cemetery is at St Avold, if that is of interest to you. You can reach the town of St Avoid from Metz or closer from Forbach by local train. Metz was the US strategic objective when the armistice was signed on 11 Nov.
The largest US military cemetery in terms of WWI deaths is at Romagne, in the Meuse Argonne. It's rather out of the way.
Per Google, St. Avold is the largest US military cemetery in terms of WW2 deaths.
I have visited both (as well as St. Mihiel). All are very poignant. I so wish as many American could visit these cemeteries as the military cemetery at Omaha Beach.
Sorry...I stand corrected. Obviously, I have not seen the place, only was at Forbach nearby and Metz.