Long Bagun (Indonesian pronunciation: [ˈlɔŋ ˈbaɡʊn]) is a district of the Mahakam Ulu Regency, East Kalimantan, Indonesia. As of 2023, it was inhabited by 15,231 people, and currently has the total area of 4,801.22 km. Its district seat is located at Ujoh Bilang, which is also known as the regency's capital.

Long Bagun is divided into the following 11 villages (kampung):

No.	Regional code (Kode wilayah)	Name	Area (km)	Population (2023)	Density (2023)	RT (rukun tetangga)
1	64.11.01.2001	Long Hurai	41.18	325	7.9/km	2
2	64.11.01.2002	Long Melaham	102.44	1,844	18.0/km	5
3	64.11.01.2003	Mamahak Ilir Memahak Ilir	638.81	1,230	1.9/km	5
4	64.11.01.2004	Mamahak Ulu Memahak Ulu	996.28	352	0.4/km	2
5	64.11.01.2005	Batu Majang	135.54	1,215	9.0/km	7
6	64.11.01.2006	Ujoh Bilang	354.73	5,218	14.7/km	15
7	64.11.01.2007	Long Bagun Ilir	74.63	886	11.9/km	4
8	64.11.01.2008	Long Bagun Ulu	567.04	1,635	2.9/km	6
9	64.11.01.2009	Batoq Kelo	1,530.76	1,056	0.7/km	4
10	64.11.01.2010	Long Merah	311.04	595	1.9/km	2
11	64.11.01.2011	Rukun Damai	12.3	875	71.1/km	5
Totals	64.11.01	Long Bagun	4,801.22	15,231	3.2/km	58

As of 2023, Long Bagun was populated by 15,231 people: 7,172 males and 8,059 females.

As of 2022, by far the largest religious group in Long Bagun were Catholics (8,899 people), followed by significant minorities including Muslims (4,483), Protestants (2,311 people), Hindus (8 people) and Buddhists (2 people).