As of February 22, 2010, a new federal law allows people who can legally possess firearms under applicable federal, state, and local laws, to legally possess firearms in this park. It is the responsibility of visitors to understand and comply with all applicable state, local, and federal firearms laws before entering this park. As a starting point, please review this PDF of Texas Firearm Regulations
Federal law also prohibits firearms in certain facilities in this park; those places are marked with signs at all public entrances.
Keep in mind that the regulations to carry a firearm do not permit the discharging of a firearm. The discharge of a firearm is still illegal in national parks.
For those on a river float trip, please be aware that it is illegal to transport firearms and ammunition into Mexico. Due to the fact that the Rio Grande is an international boundary, this is a complex regulatory area. The US/Mexico boundary is defined as the deepest part of the middle channel. As watercraft float down the river, boats cross the international border many times on a float trip. Thus, a US citizen with a firearm on the river who may lawfully possess that firearm in Texas still violates Mexican law because they likely will have entered Mexico several times during the float trip with a firearm just by meandering down the river. There are severe penalties in Mexico for the possession of firearms and ammunition,which is what a person is doing if they carry a weapon on the river. Mexican officials can arrest persons floating on the Mexico portion of the Rio Grande and along the Mexican shoreline for possession of guns and ammunition.