According to 2011 census, Kumbakonam had a population of 140,156 with a sex-ratio of 1,021 females for every 1,000 males, much above the national average of 929. A total of 12,791 were under the age of six, constituting 6,495 males and 6,296 females.The average literacy of the city was 83.21%, compared to the national average of 72.99%. There were a total of 9,519 workers, comprising 32 cultivators, 83 main agricultural labourers, 1,206 in house hold industries, 7,169 other workers, 1,029 marginal workers, 24 marginal cultivators, 45 marginal agricultural labourers, 212 marginal workers in household industries and 0 other marginal workers.
Kumbakonam has a strong Hindu majority; but it also has sizeable Muslim and Christian populations. Among Hindus, Kallars, Vanniyars, Thondaimandala Mudaliars, Brahmins and Dalits are the numerically dominant Tamil-speaking groups. Brahmins are more numerous and affluent in Kumbakonam than in other parts of Tamil Nadu. There are also large populations of Moopanars, Konars and Nadars. Amongst Muslims, the Sunnis are dominant. However, there is also a significant Shia minority. Most of the Muslims are Marakkayars or Labbays. The majority of Muslims in Kumbakonam are involved in commerce or maritime trade.Kumbakonam also has a large population of Protestant Christians largely due to the efforts of the German missionary Christian Friedrich Schwarz. The Catholics in Kumbakonam are mainly affiliated to the Roman Catholic Diocese of Kumbakonam which was separated from the Archdiocese of Pondicherry in 1899.
The population of Kumbakonam is predominantly Tamil-speaking. The commonly used dialects is the Central Tamil dialect. There are significant minorities speaking Thanjavur Marathi, Telugu, Kannada and Saurashtrian as their mother tongue.
Residential areas make up 32.09% of the town’s total area while commercial enterprises and industrial units make up 2.75% and 1.21% respectively. The non-urban portion of the town constitutes about 44.72% of the total area. Kumbakonam has a total of 45 slums with a population of 49,117.
As per the religious census of 2011, Kumbakonam had 86.07% Hindus, 9.57% Muslims, 3.99% Christians, 0.% Sikhs, 0.% Buddhists, 0.23% Jains, 0.13% following other religions and 0.% following no religion or did not indicate any religious preference.