Could you see water dripping from the toilet? If the problem was the fill valve not closing, the excess water would run into the bowl and not on the floor. Check the shutoff valve to see if it dripping and then follow up to where the line is fitted to the fill valve. Then check the tank bolts from the underside. If your tank bolts are not brass, they could rust through. I've had to replace tank bolts in the past that have rusted through and started to leak.