A quick search of a map turned up this aerial view... https://www.google.ca/maps/place/South+Fork+Dairy/@34.4052257,-102.2675889,1604m/data=!3m1!1e3!4m6!3m5!1s0x87023b3490562941:0x2d0fa006054078c0!8m2!3d34.4081115!4d-102.2630691!16s%2Fg%2F11j1kg6t_2
Using the scale, the main building appears to be about 850 x 2400 feet... so yup, about 2 million square feet.
By the way, at the google map link there are pictures of the barn during its construction (April to June, 2021)...