Tidmouth is a town situated on the River Tid Estuary, on Sodor's west coast. With a population of 35 000, it is the largest town on Sodor. It is home to the headquarters of the North Western Railway and the main line sheds.
The Tidmouth, Knapford and Elsbridge Light Railway reached the town via a road-side tramway from Knapford, which was destroyed after a gale in the autumn of 1908. A treasury grant was obtained in 1910 and a tunnel was built. In 1916 the North Western Railway completed another tunnel, this time with an extra line, and Tidmouth's value as a harbour began to be used.
The passenger station known as the "Big Station" in the books has four terminal lines and a "through" road leading to the Arlesburgh branchline, sheltered by a glass roof.
The Tidmouth station has four platforms, a glass roof, and about eight trains a day. It contains the Fat Controller's office, and is the station where HM Queen Elizabeth visited Sodor. Gordon also pulls his Express out from there every day.
The local economy mainly comes from ship-building, fishing and heavy industry.
The town's motto is "Industry and Progress".
In the television series Tidmouth has been replaced by Knapford as the big station and by Brendam as Sodor's main port, though Lower Tidmouth and Tidmouth Halt have been seen in episodes. However, Tidmouth Station can be seen on a computer game, "Thomas Saves the Day".