Chengannur (IPA: [t͡ʃeŋ:e̞n:u:r]) is a municipality in the Alappuzha district of Kerala, India. It is located 43 km (26.7 mi) south east of the district headquarters in Alappuzha and about 117 km (72.7 mi) north of the state capital Thiruvananthapuram. As per the 2011 Indian census, Chengannur has a population of 23,466 people, and a population density of 1,607/km² (4,160/sq mi).

Today, Chengannur is a primary economic and cultural hub of the Onattukara region. The town is noted for the Chengannur Mahadeva Temple and the Old Syrian Church of the ancient St. Thomas Christians community. It is also a major point for pilgrims to the Sabarimala Temple, and thus has been described as "The Gateway to Sabarimala".

The name Chengannur (chem-kunnu-ur/oor) is derived from the words 'chem' (Malayalam) which means red, 'kunnu' (Malayalam) which means hill and 'ur/oor' (Malayalam) meaning land. It means the land of red hills. The red soil of Chengannur was different from the soil of nearby regions of Mavelikara and Kuttanad.

Chengannur was a part of the Ay Kingdom in the ancient period. The Ay Kingdom's territory extended from Pamba River in the north to Nagercoil in the south. Thereafter it came under the sovereignty of the Cheraman Perumals. The earliest epigraphical record to mention Chengannur (Thiruchenkunrur) is the Mampalli copper plate inscription (947 CE) which records a donation from Venad chiefly family to the Chengannur Temple.

In the medieval age, Chengannur was controlled by the Vanjipuzha chieftains of Mundencavu, of Tulu Brahmin origin. The principality was a feudatory of Odanad. Chengannur came under the Kingdom of Travancore when the area was annexed by Marthanda Varma in 1742. Marthanda Varma transferred the rights over Chengannur from the King of Odanad to the Vanjipuzha family, after the family helped him in his conquests. The economic, social and religious esteem and the political power and sway of Vanjipuzha family over Chengannur continued to be intact throughout even the British period uninterrupted.

In the mid-18th century, there were large-scale migrations from Kollam due to various natural disasters. Black pepper was a major export item of Chengannur. Angadikkal (Angadi means market in Malayalam) was the main market in Chengannur. The current Chengannur market, known as Shastham Puram Chanda, was developed by Velu Thampi Dalawa. During the 19th and 20th centuries, this market played a major role in selling and buying goods produced in the eastern mountains with the towns along the coast.

Mahatma Gandhi addressed at the Mills Ground (Mills Maithan is Ksrtc Bus stand now) at Chengannur in 1925 as part of his visit to the Kingdom of Travancore. In 1938 as part of Indian independence movement, large gathering of people from all over Central Travancore were present at the Mills Maithan in Chengannur in response to a notification circulated by the State Congress. There was police lathi charge during the meeting and a person named 'Kutilil George' died and scores of people were injured.

Chengannur Municipality was formed in the year 1980 with Shri. P.K John Plammoottil as its First Municipal Chairman.