If that sounds like a lot, officials who released the numbers in a report on Thursday say it’s actually less than the 50,000 sites previously estimated.
The surface area of the contaminated sites is close to 225 square kilometres, or about the size of the canton of Zug.
And 10 percent of the contaminated sites are in areas used by the Swiss Army for target practice.
The findings are based on data gathered and analyzed from federal and cantonal surveys for the first time.
The survey shows that half of the polluted sites are on industrial land and 40 percent from waste discharges in addition to the 10 percent attributable to shooting ranges.
Around one percent of polluted sites are the result of accidents, the report says.
Close to 60 percent of polluted sites in Switzerland are close to usable underground water sources, according to the report.
On the plus side, the government says that two-thirds of polluted sites do not require any treatment, with around half of them posing no environmental problems.
But for 10,000 sites, investigations into their impact have yet to be done.
Studies done so far have put five percent of the sites under surveillance, while cleanup operations have been undertaken in about three percent of cases.
By the time more studies are completed over the next few years, the environment office expects cleanups will be needed at 3,000 sites on top of the 700 that have already received remediation work.
The current action to address polluted sites was kick-started by regulations dating back to the late 1990s.