A modern phenomenon has called attention to a problem with decades-old origins: places in Centennial not being called “Centennial.”

“A lot of the time, when you fill online shopping orders, it auto-populates,” Mayor Stephanie Piko said of addresses that should come up under Centennial. “It might put in Aurora for the east — on the west side, it might put Littleton.”

It's about more than a minor annoyance: Centennial fears it could be at risk of missing out on online sales tax revenue that could be incorrectly sent to surrounding cities because of the confusion.

That possibility has pushed the city to enlist the help of U.S. Rep. Jason Crow, whose office is working with the Colorado Department of Revenue, Centennial officials and the U.S. Postal Service to determine if Centennial stands to lose revenue, Crow said.

“There's the other issue independent of that, and that's of city identity. Centennial is the second-biggest city in the congressional district at 110,000 people,” said Crow, the Democrat who represents the 6th Congressional District.

Officials in cities near Centennial have talked, and they agree that having ZIP codes that follow city lines would bolster community identity, “instead of these invisible boundaries we have right now,” Piko said.

“Nineteen years later, (residents) are tired of telling people, 'No, this is Centennial,' ” said Piko, whose city was formed in early 2001.

The problem lies in the history of ZIP codes in the south metro area. Because an Englewood post office was the original one for much of the local Interstate 25 corridor and East Arapahoe Road area — including places such as the Denver Tech Center and Inverness business park — many places in the Centennial area have carried Englewood addresses, Piko said.

Likewise, because Aurora and Littleton formed long before Centennial, the new city wound up with six codes that overlap it at some point in its map, Crow said. Throughout the 1900s, other communities such as Greenwood Village, Cherry Hills Village and Foxfield incorporated, falling within ZIP code areas with “recommended” names of those older cities, according to the Postal Service's website.

This isn't the first time Centennial's addresses have sounded alarms for sales tax collection — in its first several years as a city, a total of millions in Centennial's sales tax revenue was sent to Englewood, Littleton and Aurora, Piko said. The city corrected that issue after voters approved Centennial becoming a home rule city in 2008, which allowed it to follow its own constitution, called a home rule charter, rather than the statewide municipal code.

That freed up the city to collect its own sales tax rather than relying on the state to do it, Piko said.

Online sales tax is a relatively new feature of Colorado's business landscape. In a September 2018 news release, the state announced it would require online retailers to collect sales tax after the U.S. Supreme Court's decision in South Dakota v. Wayfair Inc., which struck down the requirement that a retailer have a physical presence in a state to be required to collect sales tax. The state delayed enforcement of online sales taxes several months to give businesses time to adjust.

Centennial's look into ZIP codes is still in the process of gathering information and seeing if the city is actually losing revenue, Crow said.

The city has previously attempted to ask the Postal Service if ZIP code boundaries can be changed, but it didn't get a response, Piko said.

“The impression (was) that it takes more than just asking. The primary function of the post office is to deliver mail,” not worry about cities' tax revenue, Piko said.

She hasn't heard of mail being delayed because its address says “Centennial.” Deliveries depend on the numbered address and ZIP code, not the municipality a person writes, Piko said of her experience with the East Smoky Hill Road post office.

But Piko hopes the push to redraw boundaries might become a regional effort, and the city will be researching what a change might require and taking the first steps in talking to the Postal Service.

“And I think we would need partnership amongst the municipalities to all be asking for the same thing in this area,” Piko said. “Whether it becomes a statewide initiative is another story.”