Less than a year after announcing plans to expand its footprint in the Fulton Market District with a big new office, Google is once again searching for another huge swath of space that could make it one of the largest office users downtown.

Officials for the Mountain View, Calif.-based tech giant have been in the market in recent months talking to developers about an expansion that would roughly double its size in the trendy corridor to around 1 million square feet, according to sources familiar with the company's plans.

Sources said the company has been eyeing a series of proposed developments including 18- and 11-story office buildings planned by developer Sterling Bay at 1000 W. Carroll Ave. and 345 N. Morgan St.—both across the street from Google's Midwest headquarters—and a 13-story office building that New York-based developer Tishman Speyer and Chicago developer Mark Goodman are planning at 320 N. Sangamon St., a block east of Google's main Chicago office. Another project it has targeted in the neighborhood that is large enough to be in play is a 750,000-square-foot office building from Shapack Partners and Focus Development under construction at 167 N. Green St., sources said.

Google’s size and cachet could make any one of these planned projects. The company has been in Chicago since 2000, but its growth has picked up in the past few years. Headcount has nearly doubled to more than 1,000 since it moved from River North to Fulton Market four years ago. What once was mostly a sales operation now is more than one-third engineers.

Google's hiring plans in connection with the potential expansion and its timing are unclear, and a spokeswoman for the company couldn't be reached. But the discussions highlight the scale of Google's vision for growth in Chicago over the next few years and further validate the city's burgeoning reputation as a tech hub. It also lines up what could be a dramatically larger presence for Google in the former meatpacking district, which it helped transform into a corporate destination.

The company's hunt for more room comes just months after it announced a 132,000-square-foot lease at 210 N. Carpenter St., a new building Sterling Bay developed a couple of blocks from the roughly 372,000 square feet Google leases at its 1000 W. Fulton Market primary office. The office portions of both buildings are virtually full, which is why Google is hunting for more space in a new building.

Sterling Bay recently proposed its buildings on Carroll and Morgan, which would total nearly 750,000 square feet but still require city approval. On Sangamon, Tishman Speyer’s roughly 275,000-square-foot office building has won city approval and could break ground soon, though it may be able to meet only a portion of Google’s expansion requirement.

Google said last fall it had around 1,000 employees in Chicago, primarily in sales roles that have been a hallmark of its local team. But the company has signaled plans to beef up its local team with more engineering jobs, hoping to tap into Chicago's pool of Midwest engineering talent that is generally more affordable and easier to retain than on the coasts.

That would be in line with fellow large Bay Area-based tech companies including Facebook, Salesforce and Glassdoor that have recently signed big new leases and announced plans to add hundreds of jobs downtown. But Google—which has found a deep pool of technical talent here and is expanding on multiple fronts, from search to hardware, cloud computing and data privacy and protection—would rank among the city's biggest office users if it cracks seven figures of square footage.

By comparison, one of the city's largest companies, United Airlines, recently renewed its lease in Willis Tower for more than 850,000 square feet, one of the largest leases of contiguous office spaces downtown.

Google has recently done big real estate deals to scale its team in other major markets far from Mountain View. The company last year announced plans for a new 1.7 million-square-foot campus in Manhattan that will add to its massive Chelsea Market office. In Boston, the company is reportedly eyeing a large expansion of its Kendall Square offices near the Massachusetts Institute of Technology.

Another factor in Google's Chicago search is the fast-moving pace of leasing and development in Fulton Market, where companies are clamoring to move in and developers are proposing a flood of new office buildings. Given the popularity of Fulton Market, developers in the immediate vicinity of Google's main Chicago office may have other leasing prospects that could box out Google from meeting its long-term space requirement within a block or two of its main Chicago office.

Tech behemoths like Google and locally-grown tech start-ups have been a key demand driver for office spaces downtown. The growth of the local tech scene has helped keep vacancy relatively static for more than two years at around 13 percent, according to data from real estate services firm CBRE.

That demand trend will need to continue to keep pace over the next few years with a flurry of new office projects in the works in Fulton Market as well as new office skyscrapers under construction or planned on Wacker Drive, next to Union Station and at Wolf Point.