Carrying weapons on federal property is entirely under the purview of federal law. That being said, there are different laws and regulations, depending on where you are.
1. Federal Buildings
Buildings operated by Federal Agencies, such as the IRS, SSA, USDA, etc., and Federal Courts fall under the following law:
18 USC § 930
(a) Except as provided in subsection (d), whoever knowingly possesses or causes to be present a firearm or other dangerous weapon in a Federal facility (other than a Federal court facility), or attempts to do so, shall be fined under this title or imprisoned not more than 1 year, or both.
(b) Whoever, with intent that a firearm or other dangerous weapon be used in the commission of a crime, knowingly possesses or causes to be present such firearm or dangerous weapon in a Federal facility, or attempts to do so, shall be fined under this title or imprisoned not more than 5 years, or both.
(c) A person who kills any person in the course of a violation of subsection (a) or (b), or in the course of an attack on a Federal facility involving the use of a firearm or other dangerous weapon, or attempts or conspires to do such an act, shall be punished as provided in sections 1111, 1112, 1113, and 1117.
(d) Subsection (a) shall not apply to—
(1) the lawful performance of official duties by an officer, agent, or employee of the United States, a State, or a political subdivision thereof, who is authorized by law to engage in or supervise the prevention, detection, investigation, or prosecution of any violation of law;
(2) the possession of a firearm or other dangerous weapon by a Federal official or a member of the Armed Forces if such possession is authorized by law; or
(3) the lawful carrying of firearms or other dangerous weapons in a Federal facility incident to hunting or other lawful purposes.
(1) Except as provided in paragraph (2), whoever knowingly possesses or causes to be present a firearm or other dangerous weapon in a Federal court facility, or attempts to do so, shall be fined under this title, imprisoned not more than 2 years, or both.
(2) Paragraph (1) shall not apply to conduct which is described in paragraph (1) or (2) of subsection (d).
(f) Nothing in this section limits the power of a court of the United States to punish for contempt or to promulgate rules or orders regulating, restricting, or prohibiting the possession of weapons within any building housing such court or any of its proceedings, or upon any grounds appurtenant to such building.
(g) As used in this section:
(1) The term “Federal facility” means a building or part thereof owned or leased by the Federal Government, where Federal employees are regularly present for the purpose of performing their official duties.
(2) The term “dangerous weapon” means a weapon, device, instrument, material, or substance, animate or inanimate, that is used for, or is readily capable of, causing death or serious bodily injury, except that such term does not include a pocket knife with a blade of less than 21/2 inches in length.
(3) The term “Federal court facility” means the courtroom, judges’ chambers, witness rooms, jury deliberation rooms, attorney conference rooms, prisoner holding cells, offices of the court clerks, the United States attorney, and the United States marshal, probation and parole offices, and adjoining corridors of any court of the United States.
(h) Notice of the provisions of subsections (a) and (b) shall be posted conspicuously at each public entrance to each Federal facility, and notice of subsection (e) shall be posted conspicuously at each public entrance to each Federal court facility, and no person shall be convicted of an offense under subsection (a) or (e) with respect to a Federal facility if such notice is not so posted at such facility, unless such person had actual notice of subsection (a) or (e), as the case may be.
As stated, you cannot carry any weapon into a federal building. There are a few exceptions and some have argued that self defense or having a CPL constitutes a "lawful purpose." At this time, the government and the courts have disagreed. The notices found at these buildings will typically contain language indicating that a CPL does not allow you to carry on federal property. The language of the statute does not include parking lots. In my experience, if you bring a weapon and it gets tagged by security when you are going in, they will tell you to go put it in your car and come back.
2. The Post Office
Besides the statute listed above, there is a regulation that applies to just the PO.
39 C.F.R. § 232.1(l)
Weapons and explosives. Notwithstanding the provisions of any other law, rule or regulation, no person while on postal property may carry firearms, other dangerous or deadly weapons, or explosives, either openly or concealed, or store the same on postal property, except for official purposes.
If you have ever looked around a PO, you will find this posted. It is more inclusive than the statute, as it includes all PO property, including the parking lot. At present, there is an exception. In Bonidy v. USPS
, a US District Ct. found the parking lot provision to be unconstitutional. Unfortunately for us, this only applies to Colorado, as District Court precedent only applies to that district. Ideally, this will move up and be affirmed by higher courts and apply to larger areas.
3. National Parks and National Wildlife Refuges
This is one area where state law is important. Under Federal Regulations, you can carry in these places if it would allowable under state law. See 36 CFR 2.4:
(h) Notwithstanding any other provision in this Chapter, a person may possess, carry, and transport concealed, loaded, and operable firearms within a national park area in accordance with the laws of the state in which the national park area, or that portion thereof, is located, except as otherwise prohibited by applicable Federal law.
50 CFR 27.42
(e) Notwithstanding any other provision in this Chapter, persons may possess, carry, and transport concealed, loaded, and operable firearms within a national wildlife refuge in accordance with the laws of the state in which the wildlife refuge, or that portion thereof, is located, except as otherwise prohibited by applicable Federal law.
Here is a pamphlet
from the US Park Service on the subject. Please note that other federal laws still apply, including the ban on weapons in federal buildings. Therefore, you may not carry a weapon into Ranger Stations, Visitor Centers, bathrooms, or any other US Government building
on these properties.
4. Indian Reservations
This is governed by tribal law. There are a number of online lists, including this rather extensive one from the Handgunlaw
site. They recommend, and I agree completely, that you contact someone in authority and clarify what the rule is, preferably in writing.
5. US Army Corps of Engineers
See this pamphlet
. Weapons are not allowed, except if they are unloaded and stored in a vehicle. This applies to any land owned by the Corps of a Engineers.
If I have missed anything, please let me know.