Japan's population totaled an estimated 127.79 million as of last Oct. 1, a decrease of 259,000, or 0.2 percent, from a year earlier, government data showed Tuesday.
The year-on-year fall was the largest since 1950, the Internal Affairs and Communications Ministry said.
Of the total, Japanese nationals stood at 126.18 million, down 0.16 percent.
The population of Fukushima Prefecture, hit hard by the March 2011 earthquake, tsunami and subsequent nuclear crisis at the Fukushima No. 1 power plant, decreased as much as 1.93 percent, to 1,990,000. It was the steepest decline on record for any prefecture.
Of the nation's population, people 65 or older accounted for 23.3 percent of the total, up 0.3 percentage point and hitting an all-time high. This percentage remained the highest level in the world, exceeding Germany's 20.6 percent and Italy's 20.3 percent.
Meanwhile, people 14 and younger accounted for 13.1 percent of the total, the lowest since 1950.
The estimations were based on the 2010 national census.