South Florida — particularly Miami-Dade County — has long been the land of missed opportunity for Walmart.

Walmart may be the world’s largest grocer, but in South Florida the company is a distant No. 3 when it comes to marketshare behind market leader Publix and the second place Winn-Dixie.

It’s not for a lack of bargain-hunting shoppers. To see the potential market demand, all it takes is a visit to the supercenter in Hialeah Gardens or the newly expanded supercenter in Doral, where the two mayors have a friendly rivalry going about whose store is the biggest in the country.

Sales volumes at both stores consistantly rank among the top three to five Walmarts in the U.S. and possibly the world. Hialeah Gardens Mayor Vioset De La Cruz has been told his store took home the top spot with sales that hit $200 million last year. Ever since the Hialeah Gardens supercenter opened 12 years ago, the football field sized parking lot has been packed day or night, with traffic that can climb as high as 8,000 visitors on a busy weekend day.

With numbers like that you would expect Walmart would have spent the last decade on an aggressive expansion push. Instead, South Florida is the only market in the Southeastern United States where Walmart’s grocery market share ranks a distant third at 11.6 percent, according the The Shelby Report, a grocery industry trade publication. Walmart currently doesn’t have a single store in the city of Miami.

But that’s changing. Walmart is cranking up its growth in South Florida and especially Miami-Dade County. While most of the retailer’s stores have historically been around the edges of Miami-Dade County, Walmart is now trying to move into the heart of the city of Miami and creating controversy along the way. A supercenter proposed for the Shops at Midtown Miami has drawn the ire of some vocal local residents, but a Neighborhood Market store in Miami’s Flagami area has been more well-received.

These openings are part of Walmart’s largest expansion in the tri-county area in about seven years with 12 new stores planned, plus the expansion or relocation of seven existing stores that will be adding groceries. All Miami-Dade stores already have groceries, and Walmart will finish adding groceries in Broward by 2014.

In total, Walmart expects to invest $380 million in South Florida over the next two years and create at least 2,900 new jobs, said Martin Mundo, senior vice president for the Florida division.

“There is an opportunity in the market, and clearly we are going after it,” Mundo said. “Our customers are telling us they want our stores closer to their community. We are working hard to catch up.”

And local real estate brokers say this is only the beginning. Walmart is still hunting for expansion opportunities for both traditional supercenters and the smaller grocery-oriented Neighborhood Market. Brokers say the company has deals in the works that stretch from the city of Miami to the former Hollywood Fashion Center and beyond.

“They’re really trying to make a statement in South Florida,” said Jimmy Tate, the developer who put together the site for Walmart’s Neighborhood Market on the site of the former Everglades Lumber yard in Miami. “They’ve definitely been missing the boat in the past, but now they’re really focused down here. Walmart is looking to increase its presence here across the board. I think they’re going to challenge a lot of the local supermarkets.”