okay, if I have a square, and know the square footage-how can I find the middle of that square? I can't figure this out for the life of me.

If you know the area, take the √ of that area to get the length of the sides,

e.g. area = 500 cm^2
side = √500 = 22.36

now you want the length of the diagonal, which is the hypotenuse.
h^2 = side^2 + side^2
h^2 = 2(side^2)

e.g.
h^2 = 22.36^2 + 22.36^2 = 1000
h = √1000 = 31.6227

The middle of that square is 1/2 way down the hypotenuse or the diagonal, which would be 15.8 for my example.

The above is the explanation, here is the shortcut :

double your area
take square root of that
take 1/2 of that answer