| No. | Code | District Name | District Headquarters | C.D. Blocks | Population
| Area
| Density
| Map |
| 1 | AR | Araria | Araria |
| 2,811,569 | 2,829 | 991 | |
| 2 | AW | Arwal | Arwal | Arwal Kaler Karpi Kurtha Sonbhadra Banshi Suryapur | 699,000 | 637 | 918 | |
| 3 | AU | Aurangabad | Aurangabad | Aurangabad Barun Daudnagar Deo Goh Haspura Kutumba Madanpur Nabinagar Obra Rafiganj | 2,540,073 | 3,303 | 769 | |
| 4 | BA | Banka | Banka | Amarpur Banka Barahat Belhar Bounsi Chandan Dhoraiya Fullidumar Katoria Rajoun Sambhuganj | 2,034,763 | 3,018 | 533 | |
| 5 | BE | Begusarai | Begusarai | Bachhwara Bakhri Balia Barauni Begusarai Bhagwanpur Birpur Cheria Bariarpur Chhorahi Dandari Garhpura Khodawandpur Mansurchak Matihani Naokothi Sahebpur Kamal Samho Akha Kurha Teghra | 2,970,541 | 1,917 | 1,222 | |
| 6 | BG | Bhagalpur | Bhagalpur | Bihpur Gopalpur Goradih Ismailpur Jagdishpur Kahalgaon Kharik Narayanpur Nathnagar Naugachhia Pirpainti Rangra Chowk Sabour Sanhaula Shahkund Sultanganj | 3,037,766 | 2,569 | 946 | |
| 7 | BJ | Bhojpur | Arrah | Arrah Agiaon Barhara Bihiya Charpokhari Garhani Jagdishpur Koilwar Piro Sahar Sandesh Shahpur Tarari Udwantnagar | 2,728,407 | 2,473 | 903 | |
| 8 | BU | Buxar | Buxar | Buxar Brahmapur Chakki Chausa Chaugain Dumraon Itarhi Kesath Nawanagar Rajpur Simri | 1,706,352 | 1,624 | 864 | |
| 9 | DA | Darbhanga | Darbhanga | Alinagar Bahadurpur Baheri Benipur Biraul Darbhanga Sadar Gaura Bauram Ghanshyampur Hanuman Nagar Hayaghat Jale Keoti Kiratpur Kusheshwar Asthan East Kusheshwar Asthan Manigachhi Singhwara Tardih | 3,937,385 | 2,278 | 1,442 | |
| 10 | EC | East Champaran | Motihari | Adapur Areraj Banjaria Bankatwa Chakia Chiraiya Dhaka Ghorasahan Harsidhi Kalyanpur Kesaria Kotwa Madhuban Mehsi Motihari Narkatia Paharpur Pakri Dayal Patahi Phenhara Piprakothi Ramgarhwa Raxaul Sangrampur Sugauli Tetaria Turkaulia | 5,099,371 | 3,969 | 991 | |
| 11 | GA | Gaya | Gaya | Gaya Town Amas Atri Banke Bazar Barachatti Bathani Belaganj Bodh Gaya Dobhi Dumaria Fatehpur Guraru Gurua Imamganj Khizirsarai Konch Manpur Mohanpur Muhra Paraiya Sherghati Tan Kuppa Tekari Wazirganj | 4,391,418 | 4,978 | 696 | |
| 12 | GO | Gopalganj | Gopalganj | Baikunthpur Barauli Bhorey Bijaipur Gopalganj Hathua Katiya Kuchaikote Manjha Pach Deuri Phulwaria Sidhwalia Thawe Uchkagaon | 2,562,012 | 2,033 | 1,057 | |
| 13 | JA | Jamui | Jamui | Barhat Chakai Gidhour Islampur Aliganj Jamui Jhajha Khaira Laxmipur Sikandra Sono | 1,760,405 | 3,099 | 451 | |
| 14 | JE | Jehanabad | Jehanabad | Ghoshi Hulasganj Jehanabad Kako Makhdumpur Modanganj Ratni Faridpur | 1,125,313 | 1,569 | 963 | |
| 15 | KH | Khagaria | Khagaria | Alauli Baldaur Chautham Gogri Khagaria Mansi Parbatta | 1,666,886 | 1,486 | 859 | |
| 16 | KI | Kishanganj | Kishanganj | Bahadurganj Dighalbank Kishanganj Kochadhaman Pothia Terhagachh Thakurganj | 1,690,400 | 1,884 | 687 | |
| 17 | KM | Kaimur | Bhabua | Adhaura Bhabua Bhagwanpur Chainpur Chand Durgawati Kudra Mohania Nuaon Ramgarh Rampur | 1,626,384 | 3,363 | 382 | |
| 18 | KT | Katihar | Katihar | Amdabad Azamnagar Balrampur Barari Barsoi Dandkhora Falka Hasanganj Kadwa Katihar Korha Kursela Manihari Mansahi Pranpur Sameli | 3,071,029 | 3,056 | 782 | |
| 19 | LA | Lakhisarai | Lakhisarai | Barahiya Chanan Halsi Lakhisarai Pipariya Ramgarh Chowk Surajgarha | 1,000,912 | 1,229 | 652 | |
| 20 | MB | Madhubani | Madhubani | Andhra Tharhi Babubarhi Basopatti Benipatti Bisfi Ghoghardiha Harlakhi Jainagar Jhanjharpur Kaluahi Khajauli Ladania Lakhnaur Laukahi Madhwapur Madhubani Pandaul Phulparas Rahika Rajnagar | 4,487,379 | 3,501 | 1,020 | |
| 21 | MG | Munger | Munger | Asarganj Bariarpur Dharhara Haveli Kharagpur Jamalpur Munger Sangrampur Tarapur Tetia Bambar | 1,367,765 | 1,419 | 800 | |
| 22 | MP | Madhepura | Madhepura | Alamnagar Bihariganj Chousa Gamhariya Ghelardh Gwalpara Kumarkhand Madhepura Murliganj Puraini Shankarpur Singheshwar Udakishunganj | 2,001,762 | 1,787 | 853 | |
| 23 | MZ | Muzaffarpur | Muzaffarpur | Aurai Block Bandra Bochaha Gaighat Kanti Katra Kurhani Marwan Minapur Muraul Motipur Musahri Paroo Sahebganj Sakra Saraiya | 4,801,062 | 3,173 | 1,180 | |
| 24 | NL | Nalanda | Bihar Sharif | Asthawan Bena Biharsharif Bind Chandi Ekangarsarai Giriyak Harnaut Hilsa Islampur Karai Parsurai Katrisarai Nagarnausa Noorsarai Parwalpur Rahui Rajgir Sarmera Silao Tharthari | 2,877,653 | 2,354 | 1,006 | |
| 25 | NW | Nawada | Nawada | Akbarpur Govindpur Hisua Kashichak Kawakol Meskaur Nardiganj Narhat Nawada Pakribarawan Rajauli Roh Sirdala Warisaliganj | 2,219,146 | 2,492 | 726 | |
| 26 | PA | Patna | Patna | Patna Sadar Athmalgola Bakhtiarpur Barh Belchi Bihta Bikram Danapur Daniyawan Dhanarua Dulhin Bazar Fatuha Ghoswari Khusrupur Maner Masaurhi Mokama Naubatpur Paliganj Pandarak Phulwari Sharif Punpun Sampatchak | 5,838,465 | 3,202 | 1,471 | |
| 27 | PU | Purnia | Purnia | Amour Baisa Baisi Banmankhi Barhara Kothi Bhawanipur Rajdham Dagarua Dhamdaha Jalalgarh Kasba Krityanand Nagar Purnia East Rupauli Srinagar | 3,264,619 | 3,228 | 787 | |
| 28 | RO | Rohtas | Sasaram | Akorhi Gola Bikramganj Chenari Dawath Dehri Dinara Karakat Kargahar Kochas Nasriganj Nauhatta Nokha Rajpur Rohtas Sanjhauli Sasaram Sheosagar Suryapura Tilauthu | 2,959,918 | 3,850 | 636 | |
| 29 | SH | Saharsa | Saharsa | Banma Itahri Kahara Mahishi Nauhatta Patarghat Salkhua Sattar Kataiya Sour Bazar Simri Bakhtiyarpur Sonbarsa | 1,900,661 | 1,702 | 885 | |
| 30 | SM | Samastipur | Samastipur | Bibhutipur Bithan Dalsing Sarai Hasanpur Kalyanpur Khanpur Mohanpur Mohiuddin Nagar Morwa Patori Pusa Rosera Samastipur Sarairanjan Shivajinagar Singhiya Tajpur Ujiyarpur Vidyapati Nagar Warishnagar | 4,261,566 | 2,905 | 1,175 | |
| 31 | SO | Sheohar | Sheohar | Dumri Katsari Piprahi Purnahiya Sheohar Tariani Chowk | 656,246 | 349 | 1,880 | |
| 32 | SP | Sheikhpura | Sheikhpura | Ariari Barbigha Chewara Ghat Kusumbha Sheikhpura Shekhopur Sarai | 634,927 | 689 | 762 | |
| 33 | SR | Saran | Chhapra | Amnour Baniapur Chhapra Dariyapur Dighwara Ekma Garkha Ishupur Jalalpur Lahladpur Maker Manjhi Marhaura Mashrakh Nagra Panapur Parsa Revelganj Sonpur Taraiya | 3,951,862 | 2,641 | 1,231 | |
| 34 | ST | Sitamarhi | Dumra, Sitamarhi | Bairgania Bajpatti Bathnaha Belsand Bokhra Choraut Dumra Majorganj Nanpur Parihar Parsauni Pupri Riga Runni Saidpur Sonbarsa Suppi Sursand | 3,423,574 | 2,199 | 1,214 | |
| 35 | SU | Supaul | Supaul | Basantpur Chhatapur Kishanpur Marauna Nirmali Pipra Pratapganj Raghopur Saraigarh-Bhaptiyahi Supaul Triveniganj | 2,229,076 | 2,410 | 724 | |
| 36 | SW | Siwan | Siwan | Andar Barharia Basantpur Bhagwanpur Hat Darauli Daraundha Goriakothi Guthani Hasanpura Hussainganj Lakri Nabiganj Maharajganj Mairwa Nautan Panchrukhi Raghunathpur Siswan Siwan Ziradei | 3,330,464 | 2,219 | 1,221 | |
| 37 | VA | Vaishali | Hajipur | Bhagwanpur Bidupur Chehra Kalan Desari Goraul Hajipur Jandaha Lalganj Mahnar Mahua Patedhi Belsar Patepur Raghopur Rajapakar Sahdei Buzurg Vaishali | 3,495,021 | 2,036 | 1,332 | |
| 38 | WC | West Champaran | Bettiah | Bagaha Bairia Bettiah Bhitaha Chanpatia Gaunaha Jogapatti Lauriya Nandangarh Madhubani Mainatand Majhaulia Narkatiaganj Nautan Piprasi Ramnagar Sidhaw Sikta Thakrahan | 3,935,042 | 5,229 | 582 | |