Do you know what kind of turtle you found?
You might want to check out the Turtle society clubs in your area or via the internet.
We have 2 box turtles that we found years ago.
Mike feeds them banana's, snails, little bit of raw fresh
fish, and vegetables.
In the summer we have separate pens outside,
nestle amoung the bushes and plants with a water pie pan.
When it warm outside they will each lay inside their own
water pan.
(They also like to dig in the dirt)
In the winter they are put in separate fish tanks in
the garage.