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 Duck's Branch Line, sheltered by a glass roof. But it is incorrectly represented during Clive Spong's illustrations most of the time as having six terminal roads, with the "through" road outside the station's 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 shipbuilding, fishing and heavy industry.
Though Tidmouth is still in the television series, it has been replaced by Knapford as the biggest station and by Brendam as Sodor's main port. It only appeared in the second and third seasons. Lower Tidmouth and Tidmouth Hault have also been seen in episodes. It was later mentioned in the seventeenth season episode, Gordon Runs Dry. The town has appeared regularly since the thirteenth season with the introduction of the Tidmouth Town Square.
- The town's motto is "Industry and Progress".