Betagi became a police station in 1938 and was upgraded to an upazila on September 14, 1983. Nothing is definitely known about the origin of the upazila name. There is hearsay that the name Betagi has been originated from the word Bedagi meaning Not Guilty. In the eighteen century, the East India Company snatched away the Zamindari title from the local influential Zamindar Mr. Ainudd in Sikder who revolted against the British for forcible salt cultivation. The company brought accusation against the Zamindar and the people of this locality mentioning them as pirates. This notion was subsequently removed when Chini Bibi, an influential lady, pleaded to the company that the people are not guilty, which in Bengali means Bedagi. The ward Bedagi was colloquially known as Betagi. The original inhabitants of this area might belong to Austric origin.