The U.S. government has 15 departments that are part of its executive branch. Each department has its own secretary (the only exception is that the Secretary for the Justice Department is called the Attorney General, but he/she still sits in the Cabinet with all the other secretaries).
Note: Employees and budgets are graded on a scale from 1 (|) to 5 (|||||).
Source: https://en.wikipedia.org/wiki/United_States_federal_executive_departments
The harder part is trying to remember which department does what. It's not as straightforward as it seems. Take the Bureau of Ocean Energy Management. Sounds like something the Department of Energy should be doing. Well, wrong! It's part of the Department of the Interior. Other agencies that are part of the "Interior" include the National Park Service and the Fish and Wildlife Service. So what about the United States Forest Service (USFS)? Surely, it is also part of the Department of the Interior? No, that's with the Department of Agriculture!
Sometimes the name of an agency steers you multiple directions. Take the National Nuclear Security Administration. You would be forgiven from thinking its part of the Security establishment. Yes it does nuclear safety, but nuclear is above all else, energy. Hence the Department of Energy. That same naming ambiguity applies to the Transportation Security Administration (TSA) – this time in reverse. If you assumed Department of Transportation, you would be wrong. Rather, the TSA now falls within Homeland Security (it was spun off from the Department of Transportation after 9/11).
Can you guess where the National Laboratories & Technology Centers sits? That scientific and research organization operates some well-known institutions like the Ames Laboratory, the Los Alamos National Laboratory, Oak Ridge National Laboratory and the Fermi National Accelerator Laboratory. You could argue for its inclusion in education, labor, commerce, defense, or even security. But the right answer is the aforementioned Department of Energy. Again, the logic seems to be that testing nuclear bombs is a bit like nuclear energy.
If the Air Force, Navy (with its Marines) and Army are part of the Joint Chiefs of Staff (with the... ugh... Space Force – thank you President Trump), surely the Coast Guard is also under the Defense Department? No, the Coast Guard doesn't get its orders from the Pentagon like the other members of the U.S. Armed Forces. It's Homeland Security. And speaking of security, what about maximum security: the Federal Bureau of Prisons must also be Homeland Security, just like Customs and Border Protection (CBP) and Immigration and Customs Enforcement (ICE)? No, federal prisons belong with the court system, at the Department of Justice.
And we could go on and on!
But don't take our word for it, renown author Michael Lewis wrote about it in his book the Fifth Risk:
Like so many United States government agencies, the Department of Commerce is seriously misnamed. It has almost nothing to do with commerce directly and is actually forbidden by law from engaging in business. But it runs the United States Census, the only real picture of who Americans are as a nation. It collects and makes sense of all the country's economic statistics—without which the nation would have very little idea of how it was doing. Through the Patent and Trademark Office it tracks all the country's inventions. It contains an obscure but wildly influential agency called the National Institute of Standards and Technology, stuffed with Nobel laureates, which does everything from setting the standards for construction materials to determining the definition of a "second" and of an "inch." (It's more complicated than you might think.) But of the roughly $9 billion spent each year by the Commerce Department, $5 billion goes to NOAA, and the bulk of that money is spent, one way or another, on figuring out the weather. [...] "Commerce is one of the most misunderstood jobs in the cabinet, because everyone thinks it works with business," says Rebecca Blank, a former acting commerce secretary in the Obama administration. [...] "It produces public goods that are of value to business, but that's different. Every secretary who comes in thinks Commerce does trade. But trade is maybe ten percent of what Commerce does—if that." The Department of Commerce should really be called the Department of Information.
He continues on about the The Department of Energy:
[It] spends a lot of time and money trying to make bombs less likely to explode when they are not meant to explode. [...] The DOE, though created in the late 1970s, largely in response to the Arab oil embargo, had very little to do with oil and had a history that went back much further than the 1970s. It contained a collection of programs and offices without a clear organizing principle. About half its budget in 2016 went to maintaining the nuclear arsenal and protecting Americans from nuclear threats. It sent teams with equipment to big public events—the Super Bowl, for instance—to measure the radiation levels, in hopes of detecting a dirty bomb before it exploded. [...] A quarter of the budget went to cleaning up all the unholy world-historic mess left behind by the manufacture of nuclear weapons. The last quarter of the budget went into a rattlebag of programs aimed at shaping Americans' access to, and use of, energy. [...] There were reasons these things had been shoved together. Nuclear power was a source of energy, and so it made sense, sort of, for the department in charge of nuclear power also to have responsibility for the weapons-grade nuclear materials—just as it sort of made sense for whoever was in charge of making weapons-grade uranium and plutonium to be responsible for cleaning up their own mess. But the best argument for shoving together the Manhattan Project and nuclear waste disposal and clean-energy research was that underpinning all of it was Big Science—the sort of scientific research that requires multi-billion-dollar particle accelerators.
And finally, the Department of Agriculture:
Its very name is seriously misleading—most of what it does has little to do with agriculture. It runs 193 million acres of national forest and grasslands, for instance. It is charged with inspecting almost all the animals Americans eat, including the nine billion birds a year. Buried inside it is a massive science program, a large fleet of aircraft for firefighting, and a bank with $220 billion in assets. It monitors catfish farms. It maintains a shooting range inside its DC headquarters. It keeps an apiary on its roof, to study bee-colony collapse. There's a drinking game played by people who have worked at the Department of Agriculture: Does the USDA do it? Someone names an odd function of government (say, shooting fireworks at Canada geese that flock too near airport runways) and someone else has to guess if the USDA does it. (In this case, it does.)
Source: Michael Lewis. The fifth risk: undoing democracy. Penguin UK, 2018. [B023]
Central Intelligence Agency (CIA)
Federal Reserve (the Fed)
Federal Trade Commission (FTC)
National Transportation Safety Board (NTSB)
Securities and Exchange Commission (SEC)
Small Business Administration (SBA)
Social Security Administration (SSA)
United States Agency for International Development (USAID)
Commodity Futures Trading Commission (CFTC)
Consumer Financial Protection Bureau (CFPB)
Federal Deposit Insurance Corporation (FDIC)
These are trick questions of course. None of them belong with the executive departments, as you would expect. They are all independent agencies, outside the control of cabinet.
Most agencies (think FBI, IRS, FDA, FAA, FEMA) sit within those 15 executive departments. However, there are a slew of so-called independent agencies that are somewhat removed from the executive branch. Never mind that their roles are often very political or that their heads are appointed by the President. These independent agencies include some well-known names, like:
Environmental Protection Agency (EPA)
Federal Communications Commission (FCC)
National Aeronautics and Space Administration (NASA)
United States Postal Service (USPS)
Corporation for Public Broadcasting (CPB)