I have a toilet on the main level of a two story house, NO basement or crawl space. Sometime during the something happened with the toilet... in the morning there was water all over the floor in the bathroom and in the hallway. What do I check first to find where the water is coming out? I have turned off the shutoff valve to the toilet. Could it be the seal?

Is the water clear and fresh, or does it look "used", like sewer water? (I.e. does it look like it's fresh water that leaked from the tank, or backed up sewage that came from the bowl?)

I have a toilet on the main level of a two story house, NO basement or crawl space. Sometime during the something happened with the toilet....in the morning there was water all over the floor in the bathroom and in the hallway. What do I check first to find where the water is coming out? I have turned off the shutoff valve to the toilet. Could it be the seal?
As Moshie has stated, The first order of business would be to ascertain exactly where the leak originated.
Turn on the shutoff to the tank and wait a minute. Now take a wad of toilet paper and rub around the area where the supply connects to the tank. Check the TP. If it's wet you've located the leak. If it's dry continue on down the supply tube to the angle stop,(shut off valve) and check each connection. This is the area that I think you'll locate the leak. Unless the toilet was used durning the night and backed up it's doubtful the seal's involved. Let me know what you find and we'll instruct you on the repair. Cheers, Tom