The creation of the new cabinet-level Homeland Security agency after 9/11 and the associated identification of a new homeland security mission to prevent, respond to, and recover from terrorist attacks, constituted the largest reorganization in the United States government since World War II.
Absent the wars, the U.S. would have spent some money on the areas we now identify as homeland security, but nowhere near as much. Between Fiscal Years 2001 and 2021, the Office of Management and Budget reports that outlays for the Department of Homeland Security totaled over $1 trillion. In the 20-year period from 2001 through 2020, homeland security expenditures were more than six times as high as they were in the previous 20 years. The percentage of the federal budget that was allocated to homeland security post-9/11 was twice the percentage in the preceding two decades.
Activities that are considered “homeland security” are carried out by the federal government as well as by local and state governments and private entities. Federal government expenditures and activities include Customs and Border Patrol, Immigration and Customs Enforcement, the Transportation Security Administration, and others. Law enforcement officers at the local and state levels make up the bulk of non-federal activities and expenditures for homeland security.
Homeland Security funding is a complicated and opaque matter, not only because of the different public and private entities involved, but also due to the vastness of DHS and because not all of federal homeland security spending goes through DHS. Homeland Security is carried out at the federal level by DHS as well as by the Department of Defense, Department of State, Department of Justice, and many others. DHS accounts for only about one-half of homeland security expenditures at the federal level. And within DHS, not all funding is for homeland security. DHS runs the Federal Emergency Management Agency (FEMA), for example, which responds to both manmade incidents and natural disasters.
If federal spending on homeland security had grown at the same rate as other (non-military) federal spending, total appropriations would have been hundreds of billions of dollars lower.
State and municipal governments also likely spent a significant amount on homeland security, but the total is difficult to calculate given a lack of government data.
(Page updated as of June 2021)