The area was tossed between kings, Nawabs, zamindars from time to time and each rule has its impact on the district of Katihar. The town has got a cosmopolitan look. It was the main center of jute industry in Bihar which attracted workers from Mithilanchal area of Bihar, Purvanchal area of UP, Magadh region of Bihar and Bhojpuri speaking belt of Bihar and people from Nepal. The people from different region flocked to this town in search of job in jute factory, match factory and flour mills. Besides the original inhabitant of Kosi-Mahananda-Ganga Region the town witnessed an influx of permanent settlers from different region of Bihar and UP. Its proximity to Jharkhand brought many adivasis close to the town.
The partition of India had its own impact on the set up of town. Many rich Muslims either migrated to West Pakistan or East Pakistan (now Bangla Desh). But majority of Muslims chose to remain where they were. Many Hindus who came durting partition chose to settle at Katihar. The migration of Hindus continued till formation of Bangla Desh. Government of India provided them with piece of land to settle now known as Ek(1) number and Do(2) number colonies. Many Bengali Hindus settled in the town wherever they found a place. These people who were once referred as refugees in their own land because of partition has contributed significantly to the culture of Katihar.Many people of Indian origin had settled in Burma (now Myanmar) were also thrown out of Myanmar and many of them chose Katihar as their final destination. Government of India built a colony for them near Purana Jute Mill, known as Burma Colony Tingachhia. But all the refugees could not be accommodated in the colony and many settled here and there.
Guru Teg Bahadur the ninth Guru of Sikh, while returning from Assam passed throgh district and many local population embraced Sikhism. The famous village is Laksmipur near Karha Gola. There is a Gurudwara in the town also and there is a sizeable population of Sikhs in the town.
There is a sizeable population of Marwari and Sindhi community who are the driving force behind the economy of Katihar. Like whole of the East and North-East India they control the trading activity in Katihar. In fact in remote villages of this District one may find a Marwari doing business.
The District itself was once the part of undivided Bengal Province and there are many original Bengali inhabitants in the villages and town. In fact there is a school Ram Krishna Mission School in the town affiliated to the West Bengal Education Board.
The people here speak, Hindi, Angika, Maithili, Bhojpuri, Bengali, Marwari, Polia etc.