Frogmorton was a village in the Eastfarthing of the Shire. It stood on the East Road, between the Three-Farthing Stone (fourteen miles to the west) and the Brandywine Bridge (twenty-two miles to the east). Immediately to the north of the village, the stream known as The Water broke into two, creating a wide watery region.
Until the War of the Ring, the village seems to have been most notable for its inn, The Floating Log. During the brief time when Saruman took over the Shire, though, it became the home of the First Eastfarthing Troop of Shirriffs, and it was here that the returning Ring-bearers were "arrested" on their journey back to Hobbiton.
The name is analyzed as frog + moor ("marshy land") + ton (town, village) obviously referring to a marshy land at the division of The Water.
There is a Frogmore in Buckinghamshire.