The Mummer's Ford is a crossing of the river Trident, along the Red Fork, in the western riverlands. Upriver of Sherrer, it has a town along its banks. The location of the Mummer's Ford has not yet been published on maps, although it may be north of Pinkmaiden Castle.
A Game of Thrones
The town is destroyed at the beginning of the War of the Five Kings by Ser Gregor Clegane's raiders from the westerlands, who have already attacked Sherrer. All of the inhabitants are killed. Ser Karyl Vance, Ser Raymun Darry, and Ser Marq Piper ride to King's Landing to inform Lord Eddard Stark, the Hand of the King.
Mad Huntsman: Lions, you call yourselves. At Sherrer and the Mummer's Ford, girls of six and seven years were raped, and babes still on the breast were cut in two while their mothers watched. No lion ever killed so cruel.
Sandor: I was not at Sherrer, nor the Mummer's Ford. Lay your dead children at some other door.