The outcome of the case could determine if Utah or North Carolina gains an additional House seat.
The census counted federal employees, including military personnel living abroad, but not private citizens.
According to the Church of Jesus Christ of Latter-day Saints, 14,124 missionaries from Utah are living abroad who were not counted.
If these citizens are counted, Utah's population might have increased enough to entitle it -- and not North Carolina -- to an extra House seat.
North Carolina edged Utah by only 856 people.
But census officials said it was nearly impossible to count private citizens living abroad due to a lack of data. And N.C. officials also are examining the suit, trying to protect the state's interests.
Ric Cantrell, spokesman for Utah Attorney General Mark Shurtleff, said, "We only have three seats in the House. An extra congressional seat would be a 25 percent increase in our representation."
North Carolina has 12 seats in the House.
Shurtleff released a statement Wednesday highlighting the importance of equal representation for equal number of people and citing former U.S. Supreme Court rulings.