But we're cautioned that no deal is done.
If the center is similar to its California operation, it would be at least 1 million square feet and involve several hundred jobs.
Sources, who declined to speak on the record, expect a site decision by spring.
Sources also say Southeast Georgia has been of strong interest to Under Armour.
An Under Armour representative said Tuesday the company cannot comment at this time.
Under Armour, a public company based in Baltimore, Md., was incorporated by Kevin Plank in 1996. Plank, chairman and CEO, started the business in 1995 when he was special teams captain of the University of Maryland football team.
Under Armour is a growing company. It expects 2013 net revenue of $2.26 billion, up 23 percent over last year, and operating income of about $260 million, up 25 percent.
As of Dec. 31, 2012, the company operated two primary distribution centers for its North American business, according to its annual Securities and Exchange Commission filing.
It operated a 703,600-square-foot facility in Glen Burnie, Md., near its headquarters, and a 1.12 million-square-foot center, through a third party, in Rialto, Calif., in Southern California.
The company says it also distributes products through a third-party logistics provider in Florida, but the SEC filing did not detail the size or location.
Under Armour operates sales and management offices and retail space in the U.S. and Canada, Panama, China and The Netherlands.
"We believe our distribution facilities and space available through our third-party logistics providers will be adequate to meet our short-term needs," said the filing.
"We may expand to additional distribution facilities in the future," it said.
As of Dec. 31, Under Armour had 5,900 employees, including 900 at its distribution facilities.
Under Armour says Plank developed the idea for the products when he tired of repeatedly changing the cotton T-shirts under his jersey as they became wet and heavy during games.
He set out to develop a shirt that would remain drier and lighter and created what came to be known as "performance apparel."
Under Armour develops, markets and distributes branded performance apparel, footwear and accessories for men, women and youth.
It says its moisture-wicking fabrications are engineered in designs and styles for nearly every climate to provide a performance alternative to traditional products.
Its products are sold worldwide and are worn by athletes from youth to professional as well as by consumers.
Under Armour says its net revenue is generated primarily from the wholesale distribution of its products to national, regional, independent and specialty retailers. It also generates net revenue from product licensing and from the sale of products through its factory house and specialty stores and websites.
Under Armour said that substantially all of its products are made by unaffiliated manufacturers. In 2012, 10 manufacturers produced about 49 percent of its products.
In general, retail companies develop distribution centers in locations that are best suited to receive the products from suppliers and then deliver them to stores and customers.
Port locations can play a critical role.
Under Armour's products are made by 27 primary manufacturers operating in 14 countries, with about 53 percent of its products manufactured in Asia, 19 percent in Central and South America, 18 percent in the Middle East and 8 percent in Mexico.
With the West Coast distribution center in the Los Angeles port area, Jacksonville and Savannah, along with other port cities, would make sense in the Southeast.
Under Armour Inc., the global sportswear company, is said to be considering a Southeast U.S. distribution center and that Jacksonville has been among the sites under review.