Where to stay in Paris?

Actually, the area around Montparnasse has a lot of reasonably priced hotels, so it is a good choice to stay. There are lots of restaurants in the area as well. With the Metro, you can get anywhere in Paris quickly. There are a thousand hotels in Paris with prices from 75 to 1000 euro per night. For just one night, I go with safe, clean, cheap. Don't be afraid to use Hotwire to score a room.

Gretchen,

If this is your first time to France, i would spend what time you can in Paris. Eventho you wont be able to do/see everything, it will get your motor running to return.

as far as where to stay others are more opinionated on that.

happy trails.

I agree with Sam. Stay near the Montparnasse station. I would check booking.com for hotels in the area. Or Hotwire as Sam suggested. Even Priceline using the name your own price option. It's just for one night after all. Enjoy your trip to France!!

I also agree with Sam that Montparnasse is the best jump off point to get to Chartres . We stayed pretty near the station on our first trip to Paris and liked the area very much . Keep in mind , that with only one day in front of your needing to be in Chartres ( about an hour and a quarter from Montparnasse ) , you could also consider bypassing a half day of jet lag time in Paris ( much as I hate to even suggest this , as Paris is one of my favorite places ) you might consider going directly ( via Montparnasse ) to Chartres and staying there . We spent a day there , seeing the cathedral and wandering the town , which was enchanting . I can't name a hotel there because we day tripped from Paris , but Chartres is beautiful , and I'm sure you would not have any issue finding a nice place to stay . Staying in Paris and going down the next day would also be fine , it depends on your perspective .

The SNCF website shows you can take a TGV fast train from the Charles de Gaulle airport station to LeMans, where you catch a regional TER train to Chartres. Total time of four hours. You make one change, at LeMans, with an hour wait so you can take a light meal if you need it. Other, longer, options are shown. http://en.voyages-sncf.com/en/ For the US, specify Antarctica as your country to avoid being bumped to RailEurope. Yes, too bad to miss Paris, but you would only have part of the afternoon and evening there with the inconvenience of another hotel.

From CDG take RER line B to Denfert-Rochereau (35 min.), add some 15 minutes to go with metro line 6 to Montparnasse-Bienvenue (direction Charles de Gaulle Etoille, what is actually Arc de Triomphe). A short walk to railwaystation Gare Montparnasse for catching the train to Chartres, travel time between 1 hour and 1½ hour.
There is also an Air France Roissy shuttle bus line 4 from CDG to Gare Montparnasse, so you get a bit of sight-seeing as well and is a good option if you are not familiar with the metro and prefer to avoid it. One way online ticket costs €16,60 per person, service every 30 minutes, duration 50 minutes if there is no delay due to traffic congestion.
This gives a rough idea what it takes to go to Chartres. Info see: parisbytrain.com / uk.voyages-sncf.com / www.lescarsairfrance.com , for the latter you can select English.