The 1968 Socio-Economic Survey by the Government of Kerala gave the population of the Nair community as 14.41% of the total population of the state, constituting for 89% of the forward caste population in the state. But various sources site figures ranging from 15%, 16%, 17.5%,[citation needed] 19%and 20%. There is also the practical difficulty of certain Nair subcastes declaring as independent caste. Out of those citizens who are eligible to vote in Kerala, 15% belong to the Nair community.

Nair population has been declining in Kerala. Some of the districts in Kerala have only a small population of Nairs. Malappuram has a Nair population of 1.8% and Kasargode has about 2.1%.

The most reliable population figures comes from two sources. The BCRC estimated Nair population at 14.47% of the total population of Kerala based on a state wide sample survey conducted for the reservation of seats in educational institutions. At the same time, the government for the same purpose, gave a figure of 15.35% based on the Census of Travancore in 1941, Census of Cochin in 1941 & Census of Malabar in 1921. This figure will be true if the population growth rate is uniform for all the ethnic groups in Kerala. But this is not the case, as according to the 1941 Census, the Total Fertility Rate varied across various ethnic groups. In 1941, Kammalas had the highest TFR at 3.88 children per woman. They were followed by Ezhavas at 3.84, Syrians at 3.79, Muslims at 3.71 and Nadars at 3.64 children per woman. On the other hand, Nairs had a TFR of only 3.63 children per woman. Below the Nairs were Pulayas and Vellalas (3.43 each), Parayas (3.23), Brahmins (3.13) and Kuravas (3.13). But the Censuses of 1941 and 1921 counted many of the Nair subcastes (Maarar for example) as independent castes, and they were not added to the Nair population.

There is no accurate way to measure the present Nair population. Household sample surveys conducted by the Kerala Statistical Institute, the last of which were in 2000, produced estimates which are:

Distribution of Nair population in Kerala.

Distribution of Nairs in Kerala - District-wise.
District Total Pop Nairs % of Pop % of Nairs
Kerala 31,838,000 4,457,000 14.0% 100.0%
Trivandrum 3,235,000 575,000 17.8% 12.9%
Quilon 2,584,000 793,000 30.7% 17.8%
Pathanamthitta 1,232,000 174,000 14.1% 3.9%
Aleppey 2,105,000 352,000 16.7% 7.9%
Kottayam 1,953,000 227,000 11.6% 5.1%
Idukki 1,129,000 111,000 9.8% 2.5%
Ernakulam 3,098,000 316,000 10.2% 7.1%
Trichur 2,975,000 223,000 7.5% 5.0%
Palghat 2,617,000 330,000 12.6% 7.4%
Malappuram 3,630,000 80,000 2.2% 1.8%
Calicut 2,878,000 504,000 17.5% 11.3%
Wynad 787,000 152,000 19.3% 3.4%
Cannanore 2,412,000 584,000 24.2% 13.1%
Kasargode 1,203,000 36,000 3.0% 0.8%

Courtesy & More informations
http://en.wikipedia.org/wiki/Demography_of_Nair_community