SEOUL—North Korea is getting bigger, older and less healthy, according to data from the country's latest census, and its fabled million-man army might have fewer than 700,000 people.

The authoritarian government in December released results of the census conducted in 2008, saying its population had climbed to 24 million people from 21.2 million in the previous census in 1993.

More details have been published by the United Nations Population Fund, which helped North Korea conduct the census and sent five teams of observers to monitor it.

Even so, it's difficult for outsiders, with so little access to the country, to be certain of the precision of North Korea's data. For decades, the government has cut off the dissemination of most information about the country. The new census numbers provide a rare glimpse of official statistics.

The census reported that North Korea's population grew at an annual average rate of 0.85% for the 15-year period, a time that included a devastating multiyear famine that analysts and foreign aid agencies estimate killed between one million and two million people.