Military Installations and Bases in the United States: Map and Overview

The United States maintains a network of military installations that spans all 50 states, several territories, and the District of Columbia, forming the physical foundation for force projection, training, logistics, and command operations. These installations range from sprawling multi-service bases covering hundreds of thousands of acres to compact reserve centers serving a single county. Understanding their classification, distribution, and governance structure is essential for service members, veterans, policymakers, and communities that host them. This page covers how installations are defined and categorized, how they operate under federal authority, the common scenarios that shape their use, and the key decision boundaries governing their establishment, expansion, or closure.

Definition and scope

A military installation is a federally owned, leased, or controlled land parcel and its associated infrastructure designated for use by one or more components of the U.S. Armed Forces. The Department of Defense (DoD) defines installations broadly through the Base Structure Report, an annual congressionally mandated inventory of the DoD's real property portfolio. According to the DoD Base Structure Report Fiscal Year 2022 Baseline, the department maintained approximately 4,400 sites worldwide, with roughly 750 installations located within the continental United States, Alaska, Hawaii, and U.S. territories.

Installations fall into several formal categories based on size, function, and branch assignment:

1. Major installations — Self-sustaining communities with permanent housing, medical facilities, schools, and full garrison support. Examples include Fort Liberty (formerly Fort Bragg, North Carolina), Naval Station Norfolk (Virginia), and Joint Base Lewis-McChord (Washington).
2. Minor installations — Facilities with a focused mission set and limited on-site support infrastructure, such as ammunition depots or training ranges.
3. Leased properties and annexes — Real property held under long-term lease rather than federal ownership, counted separately in the DoD inventory.
4. Reserve and National Guard facilities — Armories, readiness centers, and training sites that serve National Guard and Reserve components under Title 32 or state authority.

Each installation is assigned a host branch — Army, Navy, Marine Corps, Air Force, Space Force, or Coast Guard — though joint basing consolidates multiple service missions onto a single installation under one management command. The Pentagon and military headquarters coordinate installation policy through the Office of the Assistant Secretary of Defense for Energy, Installations and Environment.

How it works

Military installations operate under a garrison or installation command structure. The installation commander functions as the senior authority responsible for base operations support (BOS), which covers utilities, housing, transportation infrastructure, environmental compliance, and force protection. Garrison commands report through their respective service branch headquarters, not through operational combatant commands — a structural distinction that separates installation management from warfighting authority.

Funding flows through the Military Construction (MILCON) appropriation, a dedicated budget line separate from operations and maintenance accounts. Congress authorizes and appropriates MILCON funds annually through the National Defense Authorization Act (NDAA) and the Military Construction Appropriations Act. As structured under 10 U.S.C. § 2801, no military construction project exceeding $2 million may proceed without specific congressional authorization.

Environmental compliance is a parallel governance layer. Installations operate under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA), with the Environmental Protection Agency and state environmental agencies holding enforcement authority over contamination remediation. The DoD's Environmental Programs office tracks remediation at hundreds of formerly contaminated sites across the installation network.

Joint basing — formalized under the 2005 Base Realignment and Closure (BRAC) round — merged 26 installations into 12 joint bases, pairing Army posts with adjacent Air Force bases or Navy facilities with Marine Corps stations to reduce overhead. Joint Base San Antonio, for example, consolidated Lackland Air Force Base, Randolph Air Force Base, and Fort Sam Houston under a single installation commander.

Common scenarios

Training and force generation — The majority of domestic installations serve as training platforms. Basic training, advanced individual training, and unit collective training all occur at designated installations. The basic training and boot camp pipeline routes recruits through branch-specific installations: Army recruits train at Fort Jackson (South Carolina) or Fort Leonard Wood (Missouri); Navy recruits process through Recruit Training Command Great Lakes (Illinois); Marine Corps recruits attend either Parris Island (South Carolina) or Marine Corps Recruit Depot San Diego (California).

Power projection hubs — Installations such as Naval Station Norfolk, home to the largest naval station in the world by fleet tonnage, and MacDill Air Force Base in Florida — headquarters of U.S. Central Command and U.S. Special Operations Command — serve as operational launching points rather than primarily training sites. The unified combatant commands rely on these hubs to coordinate deployments across their assigned geographic or functional areas of responsibility.

Community and economic impact — Large installations are significant regional economic drivers. The Army's Economic Impact Analysis program calculates direct employment, payroll, and contract spending for each installation annually. Fort Liberty, for instance, reported an annual economic impact exceeding $9 billion to the surrounding North Carolina region (U.S. Army Installation Management Command, FY2023 data).

Homeporting and stationing decisions — When new weapon systems enter service, the DoD conducts Environmental Impact Statements (EIS) under the National Environmental Policy Act (NEPA) before assigning them to a specific installation. Stationing decisions for the F-35 aircraft, for example, triggered EIS processes at multiple candidate bases before final basing decisions were announced.

Decision boundaries

The most consequential decisions affecting domestic installations involve establishment, major expansion, or closure — all of which require distinct legal authorities.

BRAC process — Base Realignment and Closure rounds are the statutory mechanism for large-scale installation restructuring. BRAC authority was last exercised under the Defense Base Closure and Realignment Act of 1990 (Pub. L. 101-510), with the most recent completed round occurring in 2005. Congress must authorize a new BRAC round before any future closures can proceed through the protected process, which insulates decisions from direct congressional amendment.

Congressional notification thresholds — Under 10 U.S.C. § 2687, the Secretary of Defense must notify Congress before significantly reducing the scope of operations at a domestic installation or closing it outside the BRAC process. A reduction of more than 1,000 authorized military personnel triggers notification requirements.

MILCON vs. operations and maintenance — A critical decision boundary separates construction projects funded through MILCON appropriations from facility repair and sustainment funded through operations and maintenance (O&M) accounts. Projects categorized incorrectly between these two accounts violate the Miscellaneous Receipts Act and the Purpose Statute, creating Antideficiency Act exposure.

Federal vs. state jurisdiction — Installations held under exclusive federal jurisdiction fall outside state civil and criminal law for most purposes, while installations under concurrent or partial jurisdiction share enforcement authority with the host state. This jurisdictional distinction affects law enforcement, taxation, and environmental permitting in ways that vary installation by installation.

The broader structure of how installations fit within the full armed services framework connects base governance to branch organization, defense budget and appropriations, and the national defense strategy that sets force posture requirements.