The city will submit the challenge in June, the mayor said Sunday.
The Census Bureau reported 8,175,133 city residents last spring, a mere 2.1 percent rise from 2000. The figures have Brooklyn up by 1.6 percent and Queens with only 1,343 new residents.
The city says those boroughs were vastly undercounted -- especially their immigrants -- and its total population is about 8.4 million.
A revised count would alter state and federal funding based on population, for schools, housing, food stamps, hospitals and many other services, the New York Daily News reports.
Bloomberg said he believes census enumerators could not reach immigrants and "simply recorded their homes as vacant."
"Everything we know about these neighborhoods tells a very different story," he said. "People who have tried to find apartments in these neighborhoods can confirm that there just isn't an abundance of vacancies."