To find the perimeter of a square, we need to add up the lengths of all four sides. Since all sides of a square are equal, we can find the perimeter by multiplying the length of one side by 4.
If each side of the square is 10 feet long, then the perimeter of the square is:
$$P = 4 \times 10 \text{ feet} = 40 \text{ feet}$$
Therefore, the perimeter of the square is 40 feet.