The First Nations Junior B Lacrosse League (formerly Iroquois Nations Junior B Lacrosse League) is a box lacrosse league sanctioned by the First Nations Lacrosse Association. The league was formed in 2014 with the restructuring of the Canadian Lacrosse Association. Four teams competed in the inaugural season.
The league winner earns a spot in the Founders Cup, the national championship of Junior B lacrosse in Canada.

The first game in INJBLL history was contested between Tonawanda and Seneca on May 24, 2014 at Cattaraugus Community Center. Seneca won the game 27-4. Brandon Brooks (7 goals, 6 assists) was named Player of the Game.
The WarChiefs finished a perfect 12-0 regular season and went on to win the playoff title over Onondaga 3-1 (best-of 5 series). Seneca finished as Silver medalist at the 2014 Founders Cup, falling 14-7 to the Ontario Junior B Lacrosse League champion Six Nations Rebels.
In 2015 the league joined forces with the Montreal Junior Lacrosse League to for a 7-team league, renamed First Nations Junior B Lacrosse League. Teams play each other twice in the regular season for a 12-game schedule.
On May 16, 2015 the Montreal Shamrocks won the first-ever FNJBLL game, 6-5 over Kanehsatake Warriors. The game was played at Aréna Kevin-Lowe in Lachute, Québec.
After playing eight games in the 2015 season the Jr. Voyageurs withdrew from the league, citing player commitments.
Seneca repeated as league champion in 2015 winning the two-day playoff tournament on July 24-25 at Cattaraugus Community Center. The WarChiefs defeated Tonawanda Jr. Braves 29-3 in a semifinal before downing Onondaga Jr. Redhawks in the championship game.
Montreal Jr. Shamrocks withdrew from the league after 2015. Kanehsatake sat out the 2016 season, putting their Junior team on hiatus.
Mohawk Medicine Men joined the league for the 2017 season. Tyendinaga Thunder began league play in 2018.
Champions
2014: Seneca WarChiefs
2015: Seneca WarChiefs
2016: Seneca WarChiefs
2017: Seneca WarChiefs
2018: Seneca WarChiefs
2019: Seneca WarChiefs
2022: Onondaga Redhawks