A toilet overflow control system is provided including a secondary float chamber and secondary float. The secondary float chamber is located below the toilet water tank and behind the toilet bowl at the water level of the toilet bowl and extending upward to the bottom of the toilet water tank. A vertical rod extends upward from the secondary float and is attached to a lever on the toilet water supply valve. This allows the secondary float to turn off the water when the toilet bowl water rises above a normal level. The vertical rod is inside a tube that allows it to go through the water tank without any loss of water. The secondary float chamber is fluidically connected to the toilet bowl by a horizontal conduit located just above the toilet bowl normal water level. A rinse hose is connected to the water supply valve to allow rinse water to flow into the secondary float chamber to prevent a back flow of water into the secondary float chamber during the flush.