Mithila is a region and was a kingdom situated between the foothills of the Himalayas and the River Ganges of India (North Bihar) and inhabited by Maithili speaking people.
This region was also called Tirabhukti, the ancient name of Tirhut. The Videha or Mithila Kingdom is thought to be bounded on the north by the Himalaya, on the south the Ganges, on the east the Koshi River, and on the west the Gandaki River.
The name Mithila is believed to be derived from the mythical King Mithila. He established the capital of his kingdom at Mithilapuri. Since he was born out of body of his father, he was called Janak. After this, the Kings of Mithila were called Janak. The most famous Janak was Seeradhwaja Janaka, father of Sita. There were 52 kings in the dynasty of Videh Janak. However, archaeological evidence is lacking to realistically assess the period of their migration.
The region was originally known as Videha. The kingdom of Videha is mentioned for the first time in Yajurveda Samhita. Mithila, the capital of Videha is mentioned in Buddhist Jatakas, the Brahamanas the Puranas (described in detail in Brhadvisnu Purana and various epics such as Ramayana and Mahabharata. A list of Kings is mentioned in Mahabharata and Jatakas. All the kings we known as Videha or Janak. There were total of 52 kings in this dynasty.
During the Vedic period, Mithila was the centre of the Videha kingdom with the capital in the present day city of Janakpur. The rulers of the Videha kingdom were called Janakas.