contact your Dept of agriculture office. Speak with you County Dept as well, they will give you all info and who you need to speak with. What farm do you want? How many animals? You will have to speak with Livestock Dept of Ohio Dept of agriculture. Your local Zoning department will give specifics on barn allotment sizes as well. Under 500, and not large animals, you shouldnt have to. Also depends on how you will sell the products from your farm. If selling at a farm market or at stores, you must get certified. You can find all certification requirements on ode.org website. All depends on your location and if you have neighbors & you cannot build anything near a well in case of possible contamination.
Mind you, I JUST found out tons of info regarding this today from speaking with Dept of agriculture and chief of livestock office so I know more than I knew just by researching online.
www.agri.ohio.gov
has all forms and numbers for you