As per district Gazetteers, Darbhanga, pages 33 to 34 Darbhanga under the Oinwaras (1325-1525 AD), After a temporary period of instability, Darbhanga came under the control of the Oinwaras, also known as the Kameshwara Thakur or Sugauna Dynasty. These Hindu Chiefs were left undisturbed by the Muslim conquerors, who has by now conquered the whole of Mithila and whose exploits are indicated. The Oinwara Dynasty is noted for their encouragement of leaning and fine arts and their court served as the centre of Sanskrit belle’s letters and philosophy. Among the prominent scholars of age were Gadadhara, Sankara, Vachaspati Mishra, Vidyapati, Amartakara and Amiykara. Kameshwara, the founder of dynasty, was resident of village Oini, near Pusa Road, in the District of Darbhanga. When Hazi Ilyas of Bengal divided Tirhut into two parts, the Oinwara Raja shifted his Capital to Sugauna near Madhubani. The southern part of the district was under Hazi Ilyas and the northern part under the Oinwaras. The modern subdivision of Samastipur (originally Shamsuddinpur) was founded by Hazi Shamsuddin Ilyas of West Bengal.
Samastipur became a district in 1972 when it was split from Darbhanga district.