I grew up in the country 和 I grew up in the countryside 的差別在哪裡？如果不好說明，請提供一些例句。

That's a great question. I have often heard people say "I grew up in the county." but I have never heard someone say " I grew up in the countryside." That's probably because "the county" is describing a rural area. Where "the countryside" is generally used to describe a pretty or beautiful place.
Of course I know how to ride a horse. I grew up in the county.
She can take care of herself. She grew up in the county.
The Pennsylvania countryside is really pretty with all the red barns and black cows.
Over development is ruining the English countryside.

There also another phrase you may like. "backcountry" which refers to going off the beaten path. A place where there are no roads, no people, and you have very limited supplies. Some people like to challenge themselves by going to live in the backcounty for a week or two.