RER "C" Line schedules

RER line C (and D & E) is run by SNCF, and times can be found on the "Transilien" (Paris commuter network) website: https://www.transilien.com/

Lines A and B are run by RATP (= Régie Autonome des Transports Parisiens = Paris independent transport authority) and can be found along with métro and bus times, on the RATP website: http://www.ratp.fr/horaires/fr/ratp/rer

I would strongly recommend against driving into Paris. It is likley to be slower and a lot more stress than the RER / métro. Plus you would have to find somewhere to park, which would cost a lot. You cannot just drive around looking for parking, you need to know where you are going to park before entering the city. And then still need to use the métro to your final destination.

There's late night bus replacement at the southern end of the RER-C due to construction. Check around the time of your journey. How late do you want to leave Paris for your journey each night?

Trains run at least until midnight as far as Bretigny-sur-Orge, so you might drive there and park if you want to come back late. Its paid, I'm seeing 6-8 EUR for prepaid parking depending on how long you park.
If you are there for the better part of a week, look at the Navigo Semaine pass. It runs Monday morning to Sunday night, covers the entire Paris area (including the airports and Versailles), 22.15 EUR plus 5 EUR 1st time set-up fee and bring a 1" by 1 1/4" passport photo that gets attached to the pass.

the card you need is the Navigo Decouverte which can then be loaded with the weekly Navigo Semaine Pass. You absolutely don't want to try to drive into Paris. I assume you are staying for free with relatives or something; if not, change your lodgings to Paris.

I would do what Janet says: i.e. don't stay there if you can help it, it is FAR!! Nearly an hour on the RER C (50 minutes -- if everything's running on time).

But certainly don't drive all the way into Paris! Whatever you're saving in lodging will completely be eaten up in all-day parking fees!!!

I don't see that driving into Bretigny buys you that many more options - there might be more frequent trains late at night, but I don't think there's any single train leaving central Paris appreciably later for Bretigny than there is for Dourdan (which is the section of the line you need to get to your station).

Here is the page for RER C

https://www.transilien.com/lignes/rer-trains/rer-C

You want the schedule for Dourdan (the train on the end of your line past Norville/St German les Arpajon, which is your station). "Telecharger les fiches horaires" -- download the timetables -- then choose "Invalides - Dourdan La Fôret" - you'll need to download two timetables: "lundi au vendredi" (Monday to Friday) and "samedi, dimanche, et fêtes" - (Saturday, Sunday, and official holidays).

During the week, the last RER C leaves Invalides for Dourdan (and therefore St Germain les Arpajon) at 23:07 (11:07 pm) on Monday-Thursday, and on Fridays at 7 minutes past midnight.)

Saturdays, the last train leaves Invalides at 7 minutes past midnight. Sunday nights, at 11:07 pm.

Thanks for all the help and especially the info on last train times. We ar staying with my husband's cousin, and to NOT stay with them would be an insult. My husband has driven in Paris, and we know how difficult finding parking is. I hope the cousin can give us some info on parking locales. There will be five of us going into town each day, possibly splitting up for some of the sightseeing (3 are newbies and will want to visit sites we have been to before. I have some new ones to see, for me). We will be speaking with the cousin soon and hope to get more info on parking from him. My husband is pretty confident about the drive into town....so I guess we will see. Again, thanks for the timetable info. That may sway our decision.