There is Charles D and Orly. I'm looking at Orly, but Steve's isn't giving a direct train from Anthony to the area. Thinking of Blois as a base. If anyone has done this before, which airport did you use? And how did you get to Blois by train? Thank You in advance. :)
ORY is next to A6 which leads to A10 and the Loire Valley if you wanted to drive. CDG is on the north side of Paris and can add 1 hour to the drive time. If driving, ORY is a far easier option.
The TGVs from CDG travel to Tours or St Pierre des Corps. If your destination is Blois, you will need to take a train or drive (assuming you rent a car there) from St Pierre des Corps back northeast to Blois.
Arriving ORY gives you the option of taking a 30€ taxi either to Gare Austerlitz, from where you can take a TER train directly to Blois or to Montparnasse and a TGV to St Pierre des Corps (with the same backtrack to Blois).
Given your date of travel, I would line up all the options, compare costs, compare travel times and then make a decision.
CDG should be the cheapest and easiyst to get to. I always favor rent a car travel. Many of the Chateau of the Loire are rural. Getting their by pubic transit is going to be very time costly. Also see Chartres on the way.
There's really not much difference as to which airport you use, your travel time will be the same unless you hire a car. Getting to Blois by train involves a couple of changes of train/metro from either airport. Austerlitz to Blois usually involves a change at Orleans or good fortune (or a couple of hours wait at Austerlitz). Montparnasse to Blois involves a change at Saint Pierre des Corps (and quite possibly a wait at SPdC)
Antony is not a main line train station and so of course there is no train from there to the Loire; it is a local commuter train. You need to get to the long haul train station with links to where you want to go. If it is Austerlitze, it will cost 30 to take a cab there from Orly. There are direct trains I think from CDG to Tours which is a good Loire base; I would not drive after a long flight from the US -- it is dangerous to everyone else on the road. Take the train to Tours, spend the night and pick up a car the next morning to tour the region.
I agree with Janet's advice. Driving after an overnight flight is dangerous for yourself and others. Fly into CDG and take the TGV into Tours. From there you can rent a car in the morning, and you'll have the first afternoon/evening to explore the center of Tours.
From Orly you can take the 91.10 bus to Massy TGV for 2 EUR and get a nonstop TGV to St Pierre des Corps.
A bigger consideration, I think, is the number of flights available, cost, and travel time to the different airports. Coming from Portland, you would have to travel through JFK to get to Orly, flight costs are higher, and travel time longer. You are limited to using Delta and friends (KLM, AF). If you go to CDG, you have options of Condor and Iceland Air as well, with shorter travel time and lower cost.