Most of the locks on rivers in the United States are built for commercial traffic. like barges to navigate the river system. I know they exist and I have seen them on television, but that is all I know. Can and/or how does a person in a canoe navigate through locks on major rivers (like the Mississippi) in the US.
There is not a definitive guide for all locks, however most of the major locks in the US are run by the US Army Corps of Engineers, and they do not charge recreational boaters to pass through them. To my knowledge, all locks on the Upper Mississippi are accessible via paddling.
As for the Ohio river, you can try calling McAlpine lock and dam, and they'll be able to answer for sure what the situation is on the Ohio river.
To use the lock, when you approach the lock, there should be a section at the entrance of the concrete wall with a signal rope, hopefully well marked. Paddle up to the rope and pull it, and that will signal the lock operators. They'll then instruct you on what to do.
Going through locks is not a rapid operation, and priority is allocated to commercial traffic, so you may be waiting for awhile prior to entry.
See the following brochure for further info, it has information on the hazards and restricted areas surrounding locks: Locks and Rivers. I'd recommend reading that because since the locks are built where elevation drops the fastest, the pools, dams, and weirs around the locks can be deathtraps if you paddle where you aren't supposed to.
Bring rope 75 to 100 feet of rope. When you enter the lock, the lock master will lower a rope on a hook, put the center of your rope over the hook. Your rope is placed on the rail and you payout (double) or take in rope as the water elevation changes in the lock. When the gates open release one end of your rope and pull it all in, and you are on your way.
Some locks may both a small boat and commercial (tug boat/barge) lock. If two, the signal pull cord will be near the small boat lock.