As of the census of India 2001, Nelliyalam had a population of 41,837 comprising 20,871 males and 20,966 females, making the sex ratio (number of females per thousand males) of the town to 1,005. A total of 6,043 people were under six years of age and the child sex ratio (number of females per thousand males under six years of age) stood at 946. The town had an average literacy of 83.28%, higher than the national average of 59.5%. A total of 24,380 comprising 68.11% of the population belonged to Scheduled Castes (SC) and 1,316 comprising 3.68% of the population belonged to Scheduled tribes (ST). There were are total of 8,803 households in the town. As of 2001, Nelliyalam had a total of 16,842 main workers: 156 cultivators, 952 agricultural labourers, 55 in house hold industries and 15,679 other workers. There was a total of 1,809 marginal workers: 38 marginal cultivators, 125 marginal agricultural labourers, 25 marginal workers in household industries and 1,621 other marginal workers.