Train from Rome Airport to Assisi

All of your destinations/transits are easily reached by train

Trenitalia
https://www.trenitalia.com/content/tcom/en.html

Roma Termini- Assisi
You will take the Leonardo Express from FCO to Termini then catch train to Assisi- this will be a regional train.

Check the schedule now so you have an idea of your choices, no point purchasing in advance as you don't know if your flight will be delayed or how long Passport Control will take. Since this will be a regional train - no need to purchase in advance as the price never changes and they can't sell out. Be sure to validate your ticket.
You could also download the Trenitalia app and purchase your ticket once you have landed and are thru Passport Control-
or
Just buy your ticket at the airport station (window or kiosk) for the LE and your train to Assisi

There are trains that require no change, some require a change in Foligno.
The journey will take about 2 hours.

A private driver for that distance would be pricey- no idea for sure but I'd guess 400 euros? (the train from Termini is 13.80 euros, LE is 15 euros per person)

Once you arrive at Assisi station you can grab a taxi or the bus up to the town. (The station is well below the town)

Take a taxi to the airport- fixed rate 55 euros. Have your hotel call for one that am- it shouldn't take more than 30-40 minutes to get there. Very easy. Be in a taxi by 6:15 and you will be fine.
OR
If you are staying near Termini- take the Leonardo Express from Termini to airport. I think it runs every 15 min.

What time is your flight?

Christine,
Thank you so much. I so appreciate your info.

We are leaving from Rome to go back home on a Sunday morning at 10:15 so I'd like to arrive to airport by 7:15 am (hubby will balk at this but I'm a rule follower w/ that stuff!)
We are staying at an AirBnB that is on Piazza della Rovere. I just put in directions from there to airport and it says it's a 30 minute ride. I will reach out to the AirBnB host to see if he will be willing to call a cab for us since my Italian is not good. Is the taxi a flat fee or flat fee per person?
Any other infor you have would be greatly appreciated.

Thanks,
Joanne

First, your 10.15 flight on Sunday morning is mostly like not a direct flight back to the US rather a connecting flight somewhere else in Europe. So an 8.30, 9 am arrival is find. Take a taxi -- if is fixed rate and cheap for two. Get you hotel to call the cab. You will be fine. We have done that several times and it works well.

Take the airport train to Termini and train from there to Assisi. Either one or two changes and roughly 3 hours. Buy your tickets are the airport train station and you will be fine.

First, your 10.15 flight on Sunday morning is most likely not a direct flight back to the US rather a connecting flight somewhere else in Europe. So an 8.30, 9 am arrival is fine.

In light of the fact OP has not disclosed their US destination nor which airline they are flying, I am puzzled on what basis one could make the above statement.

Hi all,
To clarify, we will be flying on a nonstop flight from Rome back to Boston on a Sunday at 10:15.

I appreciate all your advice on there.

THanks,
JOanne