Rock River Arms is owned and operated by brothers Mark and Chuck Larson.

[3] Parting ways with Les Baer in 1993, the Larsons began to build AR-15 type rifles for Eagle Arms in Coal Valley, Illinois.

At around the same time, they began their own venture, Tolerance Plus (the name was later changed to Rock River Arms), producing custom 1911 pistols.

The Larson brothers severed their connection with Eagle Arms in 1997 when that firm moved to Geneseo, Illinois.

[7] As a result of Rock River Arms winning the DEA contract, other federal agencies, including the Federal Bureau of Investigation and United States Marshals, have also obtained Rock River Arms weapons under piggyback contracts.