Kerala districts came into existence under the States Reorganisation Act (amended by the Constitution (Seventh Amendment) Act) on 1 Nov 1956. At the time of its formation, Kerala had only five districts: Thiruvananthapuram, Thrissur, Kollam, Kottayam, and Malabar.
Prior to the States Reorganisation Act of 1956, we had the State of Travancore-Cochin (1949–1956) or ThiruKochi State, which was divided as the following to form the different districts of Kerala.
Thiruvananthapuram Division and Southern Division along with Kanyakumari merged and formed as Thiruvananthapuram district,
The entire Kochi kingdom including six Taluks and with its old capital city Thrissur got converted as the single district was named as Thrissur district,
The Kottayam which constituted the Northern Division of Travancore was renamed as Kottayam district,
The Central division of Travancore which had Kollam as its headquarters got renamed as Kollam district,
and the district of Malabar.
The district of Malabar with its 15,009 sq.km. was too large to govern. So the first Governor of Kerala, Dr. Burgula Ramakrishna Rao took the initiative to divide the Malabar region. That itself proved to be difficult, because, at that time, Kerala was under President’s rule with no elected State Government.
On 1 January 1957, based on the references of ancient medieval era Kingdoms of Malabar — Zamorin Kingdom, Kolathiri Kingdom, and Valluvanadu — the Malabar district was divided into the districts of Palakkad, Kannur, and Kozhikode.
1 Nov 1956 Kollam ,Kottayam, Thrissur,Thiruvananthapuram
1 Jan 1957 Kannur ,Kozhikode,Palakkad
17 Aug 1957 Alappuzha
1 Apr 1958 Ernakulam
16 Jun 1969 Malappuram
26 Jan 1972 Idukki
1 Nov 1980 Wayanad
1 Nov 1982 Pathanamthitta
24 May 1984 Kasargod