Announcing the findings of a census conducted last year, Economic Planning and Development Minister Absalom Dlamini said the population now stands at 1,018,449, made up of 481,428 males and 537,021 females.
The figure represents a fall of 218,672 on the last census conducted in 1997 when the official tally stood at 1,237,121.
Swaziland has been particularly badly hit by southern Africa's AIDS pandemic, with close to 40 percent of the adult population affected by the virus, according to UN figures.
Dlamini, in a speech on World Population Day, said the census also showed that 78 percent of the population lived in rural areas.
Aisha Camara, the Swaziland representative of the UN's population fund (UNFPA), said figures in the census showing that 589 out of every 100,000 women died while giving birth were a particular cause for concern.
"The findings ... show that Swaziland is among the countries that have made least progress in reducing both maternal and child mortality ... This is unacceptably high," he said.