Day trips from Paris

you can do Bayeux and Normandy in one day as long as you keep your itinerary short.

Strasbourg is another great one day trip

I've done day trips to Chartres, Chantilly and Giverny.

• Since Notre Dame burned, Chartres with it's magnificent stained glass is a substitute for a working Gothic Cathedral. (Sainte-Chapelle has wonderful stained glass but is not a "working" church.)

• Chantilly is a really interesting hunting lodge - it was raining the day I went so didn't spend much time in the surrounding outdoor spaces.

• Giverny is an easy train journey as well. This is a wonderful outing for anyone who loves either Monet or gardens.

I know many do Bayeux/Normandy for a day trip but there is so much there to me it's a shame not to give it at least 2 nights so you've got partial days in Bayeux and a full day for the Normandy landing sites.

When are you planning to travel? I'd probably only consider Chartres if you are traveling soon with the transportation strike going on. One in 3 trains is running to Chartres - about hourly, so still doable as a day trip.

What kind of sights interest you? My choices might not be what would be fun for you!

There are dozens of great day trips within an hour of Paris by train (assuming trains are running)

Small cities like Reims (Champagne houses) or Rouen or Chartres for the Cathedral. Medieval towns like Senlis, Provins, Moret sur Loing, Crecy la Chapelle. Chateaux like Versailles, Malmaison, Vaux le Vicomte, Fontainebleau, Sceaux, Rambouillet, Maintenon. Auvers sur Oise where Van Gogh lived his last. Here are a few we have done but there are so many others:
https://janettravels.wordpress.com/category/day-trips-from-paris/

Paris to the Past by Ina Caro describes 25 day trips from Paris by train (a few are so long I'd call them overnighters). Since it was published several years ago, you should check the current schedules for anything that interests you.

I'm planning on an overnight to Rouen for my trip next May.

Thank you everyone for your suggestions! We don’t go until September 2020 so I can do my research all winter on your ideas! We love renting bikes to get around so Monet Gardens sound like a great place for us to include that!
Carolyn

We'll be heading back to Reims when we get to Paris in May. But also planning to see Vaux and do some hiking on trails/parks within 60 minutes of our house.

There is a book "An Hour From Paris" by Annabel Simms with ideas, many to villages you may not have considered. Over the years we've gone to Dijon, Strasbourg, Rennes, Chartres, Rouen. So many places work for a daytrip with the public transit (assuming the strikes end). My 2 favorites are Strasbourg and Rennes, but all the cities are nice to visit.