Koothanallur is a town in Tiruvarur district in the South Indian state of Tamil Nadu. The town is located at a distance of from the district headquarters Tiruvarur and from the state capital Chennai. Koothanallur is known for the Big Mosque, a prominent Islamic shrine.
Koothanallur is believed to have obtained its name from two brothers named Koothan during the early 18th century. Koothanallur was a part of the erstwhile Tanjore district until India's independence in 1947 and Nagapattinam district until 1991 and subsequently a part of the newly formed Tiruvarur district. The town is a part of the fertile Cauvery Delta and the major profession in the town is agriculture.
Koothanallur is administered by a municipality established in 1994. As of 2011, the municipality covered an area of and had a population of 25,423. Koothanallur comes under the Tiruvarur assembly constituency which elects a member to the Tamil Nadu Legislative Assembly once every five years and it is a part of the Nagappattinam constituency which elects its Member of Parliament (MP) once in five years. Roadways are the major mode of transportation to the town and the nearest railway station is at Mannargudi. The nearest seaport is Nagapattinam Port, located away, while the nearest airport is the Tiruchirappalli International Airport, located away from the town.