If you've ever wondered which building in the United States has the most people inside, New York City's massive residential complexes and skyscrapers might come to mind.
The answer, however, depends on how "most populated" is defined.
The Pentagon in Arlington, Virginia, is one of the strongest contenders for the most people inside a single building during the workday. For overnight populations, New York's massive residential buildings and developments complicate the question.
The Bronx's Co-op City is often cited in discussions about the country's most populated residential developments. But there's a catch: Co-op City is made up of dozens of buildings rather than one structure.
Here's what to know about the most populated buildings and developments
in the United States.
What is the most populated building in the U.S.?
There isn't a definitive answer because population can vary depending on the time of day and whether the measurement includes employees, residents, visitors or people attending an event.
The Pentagon is one of the clearest examples of a building with a massive daytime population.
According to WorldAtlas, about 26,000 people are at the Pentagon each day. That includes roughly 23,000 military and civilian employees, along with about 3,000 contractors, support staff and visitors.
The Pentagon covers about 6.5 million square feet, including 3.7 million square feet of office space across five concentric rings. Its corridors stretch for about 17.5 miles.
The building also has 16 parking lots, 131 stairways and 19 escalators.
What is the most populated residential building?
Determining the most populated residential building is more difficult because there is no comprehensive database tracking how many people live in each building.
New York City is home to some of the country's largest residential buildings and developments.
Co-op City in the Bronx is often mentioned as one of the most populated residential developments in the United States. According to WorldAtlas, the development has 15,372 residential units and was home to between 43,000 and 50,000 people based on 2010 U.S. Census data.
But Co-op City isn't one building. The 320-acre development consists of 35 high-rise buildings and seven groups of townhouses.
That distinction makes it difficult to call Co-op City the most populated single building in the country.
Could a New York City skyscraper hold the most people?
One possible contender is Sky, a residential skyscraper on West 42nd Street and 11th Avenue in Manhattan.
Sky opened in 2016 with about 1,175 apartments, according to the New York Post.
The building is among Manhattan's tallest residential towers, although another New York City skyscraper, Central Park Tower, is significantly taller. Central Park Tower rises 1,550 feet but has just 170 residential units.
Sky's large number of apartments means it has the potential to house a substantial population. But without knowing how many units are occupied at any given time, it's impossible to say whether it has more residents than any other single building in the country.
What building has held the most people for an event?
If the question shifts from permanent population to the largest crowd gathered for an event, sports stadiums enter the conversation.
Michigan Stadium, home of the University of Michigan Wolverines, typically seats 107,601 people. In 2016, however, the stadium set a record when 115,109 people attended a game between Michigan and Notre Dame, according to WorldAtlas.
The record didn't last long.
On Sept. 10, 2016, a college football game between the University of Tennessee and Virginia Tech drew an even larger crowd at Bristol Motor Speedway in Tennessee. The event set a record for attendance at an American football game, according to Guinness World Records.
Bristol Motor Speedway, however, isn't a building, so it doesn't qualify when looking specifically for the most populated building in the United States.
So, which building is the most populated?
There's no definitive answer to the question.
The Pentagon is a strong contender for the largest daytime population within a single building, while New York City has several residential skyscrapers capable of housing thousands of people.
Co-op City may have one of the largest residential populations in the country, but because its residents are spread across dozens of buildings, it shouldn't be considered a single building.
Ultimately, the answer depends on whether you're counting employees, residents, visitors or event crowds — and whether you're talking about one building or an entire residential development.
This article originally appeared on Rockland/Westchester Journal News: What is the most populated building in the U.S.? A NY contender complicates the answer
