Source: Cargill.

Publicly traded companies typically get all the attention, and many times with good reason. They're the ones that have to answer to shareholders, spill the beans on the financial data, and get praised or ridiculed by analysts and individual investors alike each quarter.  

But in the U.S. there are obviously many more companies that aren't publicly traded, yet employ millions of workers, build up the country's economy, and bring in a lot of revenue. 

According to recent data from PrivCo, and first reported by 24/7 Wall Street, below are the largest private companies in the U.S. this year. So let's take a quick look at who they are and what they do:

10. Publix Super Markets Inc -- $30.6 billion in revenue
Many readers may not have had the pleasure of shopping at a Publix because their stores are located only in the South, but its limited geographical reach hasn't stunted the company's growth. Publix is the largest employee-owned grocery store in the U.S. and is the 10th largest grocery store chain in the country by sales.

The company started in 1930 with just one store but has since grown to 1,102 locations and 168,500 employees. Publix prides itself on creating a store experience "Where shopping is a pleasure" and this writer can attest that Publix employees go out of their way to help shoppers. That's likely why the company has made Forbes' "100 Best Places to Work For" list every year from 1998-2015.

9. Pilot Flying J -- $32 billion in revenue
Perhaps you've made a long trip across the country and stopped at -- or at least seen signs for -- a Pilot or Flying J travel plaza. In the old days these places would have been called truck stops, but Pilot Flying J's "travel plazas" and "travel centers" sport amenities like showers, fast-casual dining, and urgent care facilities.

What started out as just one gas station in Virginia in 1958 evolved into a massive number of truck driver destinations across the U.S., and eventually the Pilot and Flying J companies merged in 2010. Today, the company has more than 650 locations across the U.S. and Canada, with a total of 24,000 employees (including its subsidiary, Pilot Logistic Services).

Recently Pilot Flying J encountered a rough patch when the company admitted it had defrauded companies out of diesel fuel rebates, and agreed to pay $92 million back to its customers last year. Since then, Pilot Flying J has continued to expand its stores across the country, launched its new urgent care locations, and invested more than $100 million in upgrading its locations with new amenities.

8. Mars -- $35.25 billion in revenue
The story of Mars begins in a kitchen in Tacoma, Washington in 1911, where Frank C. Mars cooked up the first Mars candy that started the company. From there, Mars' son Forrest E. Mars, Sr. teamed up with him to launch the Milky Way bar, which, I'm pretty sure, has found its way into more Halloween bags than any other candy to date (it's just hunch). The Mars company expanded its empire in 2008 when it bought the Wm. Wrigley Jr. Company, including its chewing gum brands, Altoids, and Life Savers.

While Mars is best known for its candies, it also owns food brands, pet hospitals, and even symbioscience. Mars employs nearly 70,000 associates around the world and is still family owned, though it's been managed by non-family members since 2001. 

7. Liberty Mutual Holding Co., -- $39.6 billion in revenue
Insurance! Who doesn't like to read a paragraph about an insurance company, am I right? The company was started in 1912 and sells personal insurance products like automobile, home owners, and casualty policies and commercial insurance like property-casualty, group benefits and life insurance in the U.S. Meanwhile, the company's Liberty International division sells insurance all over the globe, and nearly any kind you want. (Seriously, even if you're in Russia you can buy some of the company's insurance policies -- you're welcome, Mr. Putin!). Liberty Mutual has about 55,000 employees and is headquartered in Boston, Massachusetts.  

6. Bechtel Corporation -- $42.15 billion in revenue
Bechtel's website says it's a construction, engineering, and project management company, but that barely does the company justice. Bechtel basically has its hand it nearly every kind of project that involves large, industrial equipment. Need an airport built? Done. How about a hyrdoelectric dam? No problem. Heck, the company even destroys chemical weapons!

Started in 1898 by Warren Bechtel as primarily a railroad construction company, Bechtel Corporation has grown into an international company that's helped build the Hoover Dam, upgraded the London Underground tunnels, and built gas pipelines in Algeria. The company has completed projects in 160 countries on every continent and employs about 53,000 people. Oh yeah, and it helped clean up the Three Mile Island disaster, too.

5. Health Care Service Corporation -- $55 billion in revenue
More insurance! HCSC is the largest non-investor-owned health insurer in the United States and fourth largest overall, operating through Blue Cross and Blue Shield policies. The company also has affiliates that sell disability, dental, and other insurance policies.

The company was founded in 1936 as a group of civic leaders came together in Chicago in order to establish affordable healthcare in the midst of the Great Depression, and introduced some of the first healthcare plans in the states it operates in today. HCSC operates mainly in Illinois, Montana, New Mexico, Oklahoma, and Texas, and has 15 million members and 23,000 employees.

Source: Dell.

4. Dell -- $55.49 billion in revenue
The computer giant was founded in 1984 by Michael Dell when he was just a 19-year-old college freshman. Four years later, the company went public, raising $35 million. In 1992, Dell hit the Forbes 500 list. It continued to expand quickly, becoming one of the leading PC makers worldwide.

Eventually Dell moved into the server space, notebooks, tablets and other consumer and enterprise IT solutions. In 2013, founder Michael Dell and Silver Lake Partners bought back the company from shareholders for $24.9 billion, making it a privately owned company once again.

3. State Farm Mutual Automobile Insurance Co. -- $71.2 billion in revenue
OK, we're seeing a pattern here. If you want to have one of the largest private companies in America, then start an insurance company! State Farm Mutual Automobile Insurance, unsurprisingly, started out as an auto insurance company in 1922, founded by G.J. Mecherle. Now the company sells nearly 100 different products, including banking services and mutual funds.

State Farm insures more cars and homes than any other company in the U.S., has a total of 82 million accounts and policies, and processes nearly 35,000 claims per day (Take a defensive driving class, people!). State Farm employs 65,000 people and as a mutual company the policyholders own the company. 

2. Koch Industries, Inc -- $115 billion in revenue
Named after Fred C. Koch, who developed a method for converting heavy oil into gasoline, Koch Industries is a worldwide conglomerate that has its hands in refining, biofuels, pollution control equipment, forest products, minerals, and even ranching. Koch operates in 60 countries and employs more than 100,000 people. The company has grown so large in part because of its massive reinvestment policy, in which 90% of its shareholder earnings are put back into the company.

Koch has been in a negative spotlight at times because of the political affiliations of CEO Charles Koch and brother David, a $296 million wrongful death ruling against the company in 1999, and the fact that Koch Industries ranks among the top three polluters in the U.S. 

1. Cargill Incorporated -- $134.9 billion in revenue
Topping the list of private companies is Cargill, a massive conglomerate that got its start all the way back in 1865 as a grain storage facility. Now the company is involved in everything from agricultural trading and processing, food ingredients, and meat and poultry services, as well as energy and industrial services. The company employs 152,000 people across 67 countries, and its annual revenue would easily surpass most of the largest publicly traded companies.