We will be spending 4 days in Amsterdam in early October-we will miss the tulips, but is there a way to get a feel for the Dutch coutryside (windmills etc) on a day trip from Amsterdam? Thanks

You could still go to the gardens at Keukenhof..much more than just bulb flowers.

Zaans Schanz for windmills you can go INSIDE of

Keukenhof is closed from mid May to Mid March. So that's out.

Zaansche Schans is a possibility, easy to get to by train, or Kinderdijk, further away, but much better imho.
You could combine Zaansche Schans with Volendam but both are pretty touristy. There are bus trips you can book in Amsterdam to take you to such places.
Or take a train up to Enkhuizen and visit the Zuiderzee museum.
Naarden is a lovely old fortified town, combine that with Muiden and Muiderslot. No Windmills but interesting to visit.
Or go out to Hoge Veluwe NP and ride the white bikes trough the park, and visit the Kroller Muller museum while you are there. Again no windmills, but still Dutch countryside - just not what most people think of as Dutch countryside .

Thanks for the feedback will continue to research and will use your ideas as a starting point

We went on a half day bike tour with Mikes Bikes that went outside of Amsterdam - we saw some windmills, stopped at a farm where they make cheese and wooden shoes, rode along some country roads, etc. It was a lot of fun.