Hi Kay & Thank You!
The counter is just 2 oak boards that we picked up at Home Depot stained and clear coated, they are 31 1/2" deep so that I could put things on the back of the counter and still have plenty of room to scrap a 12x12 layout :)
The two filing cabinets that you see on each end are actually almost as deep as the counter so they are the main support and then the floss cabinet that you see in the middle (sitting on a wooden crate from Michele's) is also acting as a support. since the filing cabinet and crate are not as deep my husband also put a 2x4 board in the back of it that goes from the floor up to the bottom of the counter. The seam from the 2 boards actually runs down the middle of the counter under the green lace table runner that you see ;)
You could also support the counter by using the craft cubes from Michele's that you see on the top of my counter, when you stack them 2 high they are the perfect height for a counter, if you gave yourself enough space on both ends of the counter to open drawers you could point the drawers out and run them all along the sides (did that make sense lol) I hope all this helped and if you have any other questions please feel free to ask :)