Katihar district is a district of Bihar state situated in its north eastern region. The administrative headquarters of the district is located in the Katihar city. In the ancient time, the Choudhary family, who were the biggest landlords of Kosi zone, had a strong hold over the district. Khan Bahadur Choudhary Mohammad Baksh was the founder of Choudhary family and after his death, his successors called Choudhary Taj Mohammad and Choudhary Mohammad Ashraf were also started to live in a haweli named Taj Dehori like a landlord. During the period of British rule, the place of Katihar went into the hands of Zamindar’s rule and Nawab were the Indians who were helping British to rule over farmers, labour classes, etc. Before the partition of Bengal, Katihar was a part of the Bengal. But the Partition led to the division of Bengal into Bihar, Bengal and Orrisa where as present day's Katihar disrict came under Bihar. When the entire country was challenged by the British rule, at that time Katihar was there in the fore front of the agitation. The natives of Katihar also got its independence along with all the Indians. Katihar became a sub-divisional town of Purnia district on 2nd October, 1973. In the same year i.e. 1973 it was split from the Purnia district and in the year 1976 Katihar was emerged as a separate district in the map of Bihar.

Geographically, the district lies at 25°54'N latitude, 87°57'E longitude and 20 m Altitude. In the year 2021, there was a total 2.03% forest area of total geographical area. The district encompasses a geographical area of 3057 sq. km. and it is bounded by Purnia district on the north and west, Jharkhand state on the south, West Bengal state on the east and Bhagalpur district on the south west. Most of the rainfall in the district occurs during the monsoon season. The actual rainfall in the district was 1620.0 mm in the year of 2021-22.

Administration wise, the district is divided into 3 sub-divisions namely Katihar, Barsoi and Manihari. There are 1 Lok Sabha seat and 7 Assembly constituencies in the district. Moreover, the district comprises 3 towns and 1,540 villages. The administrative language in the district is Hindi.

According to 2011 census the district has a population of 30,71,029 out of which 16,00,430 are males and 14,70,599 are females. The district has a sex ratio of 919 females for every 1000 males. During the year 2001-2011 the population growth rate in the district was 28.35% including 28.36% were males and 28.35% were females. As per 2011 census the major religions in the district are Hindu and Muslim with 54.85% and 44.47% of the total population. The population density in the district is 1,005 persons per sq. km. According to 2011 census the principal languages in the district are Hindi and Urdu with 73.91% and 9.11%. In the year 2020 the number of live births in the district was 96,129 out of which 49,907 were males and 46,214 were females. In the same year the number of deaths in the district was 10,376 out of which 6,590 were males and 3,785 were females.

More than half of the population in the district are engaged in agriculture. Some of its chief agricultural products are paddy, jute, etc. Every year a huge chunk of revenue comes from these agricultural products. In case of industries, the district is not so develop. Only some jute and paper mills can be found in the district. In 2006 the Ministry of Panchayati Raj declared Katihar as one of the country's 250 most backward districts and currently receiving funds from the Backward Regions Grant Fund Programme (BRGF). In the year 2011-12 the gross domestic product in the district was Rs. 5,38,543 lakh at current price and Rs. 3,25,375 lakh at constant prices in the year 2004-2005. In the year 2011-12 the net domestic product in the district was Rs. 4,82,080 lakh at current price and Rs. 2,87,035 lakh at constant prices in the year 2004-2005.

As per 2011 census the literacy rate in the district is 52.24% out of which 59.36% are males and 44.39% are females. The number of literates in the district is 12,80,190 including 7,62,256 are males and 5,17,934 are females. Katihar can boast of educational institutions of repute such as Katihar Ramakrishna Mission, Vidyamandir, which has its inception in the year 1951, and can be considered as the oldest institution in the city. In addition to this, there are other institutions like Kendriya Vidyalaya, Scottish Public School, Netaji Vidyamandir, AAM children Academy, Ramakrishna Mission, etc which imparts quality education to the children. Katihar Medical College and Hospital, A to Z Educational and Welfare Trust are some other institutions which are educating as well as training students through regular courses.

The district has a set of tourist place which allures numerous from different parts of the world. Some of its prominent tourist spots are the Goga Lake, Gandhi Ghar Kursela, Bhairav Nath Mandir, Guru Tegh Bahadur Gurudwara, Pir Mazar, Satsang Mandir, and Gorakh Nath Mandir, Gauri Shankar Mandir and Durga Mandir.