Chattanooga, Tennessee, has citywide free internet; Phoenix is only a 90-minute flight from San Francisco; and Chicago has the most profitable startups.

Cities outside major hubs like New York and San Francisco are pitching all kinds of perks, including lower cost of living and cheaper wages, to attract companies. And, according to Inc. 5000 data, some companies are hiring like crazy in these secondary metro areas.

When we took a closer look at this year's data--which canvases the fastest-growing private companies in America--the metro areas where Inc. 5000 companies' total work force in 2015 had grown the most compared with 2012 were dominated by the usual suspects. The top five were L.A., Philadelphia, New York, D.C., and Atlanta, respectively. (Notably absent from the top 10 is San Francisco, which came in at No. 16.)

No. 6 just might surprise you. Companies calling the gateway to the Great Smoky Mountains--also known as Knoxville, Tennessee--home, reported growing their ranks by 25,509 in the past three years.

Of course, the Inc. 5000 looks at all fast-growing private companies, regardless of their industry. That includes human resources firms. And it just so happens that the Knoxville-based staffing firm AtWork Group (No. 2,605) was a big job creator over the past three years, adding 25,000 jobs at its client companies over the term.

It's something of an inconvenience of the data, which is self-reported by the companies, but also, these firms naturally are giant hiring machines. But head counts at human resources companies may be overrepresented, as employees on the payroll might not include actual company employees. In other words, these companies tend to skew the numbers.

Even so, other lesser-known startup hubs bubbled up with some impressive numbers, without HR companies propping them up. Among them, firms in the Dallas-Fort Worth Texas metro area have added 22,095 jobs since 2012, and companies based in the Phoenix metro area grew ranks by 11,491 jobs in the past three years.

As for the big cities, the hiring binge was similarly sweet. The Philadelphia metro area--which added 57,000 new jobs--beat out New York thanks to Freedom Mortgage (No. 1,904), a financial services firm that hired more than 1,600. TechStyle Fashion Group (No. 679), an online retailer based in the Los Angeles metro area, hired nearly 1,900 employees, and C2 Education (No. 2,281), which is based in Duluth, Georgia, in the Atlanta metro area, hired just over 2,700.

Employee numbers are self-reported by each company as of the last day of 2015. Inc.'s compares this data with that of year-end 2012. The definition of an employee includes seasonal workers receiving any level of benefits, such as basic paid national holidays.