* The sticker on the driver's side doorjamb: This sticker will list the recommended tire size and inflation pressure.
* Your owner's manual: The owner's manual will also specify the correct tire size.
* The sidewall of your existing tires: The size is printed on the sidewall of each tire. It will be a series of numbers and letters (e.g., P225/70R15).
Without knowing your specific Town & Country's trim level and options, I can't give you a definitive answer.