Simplify the following text for a Grade 10 native English-speaking person.
Original: The eight Harbin counties originally formed part of Songhuajiang Prefecture , and became incorporated into Harbin on 11 August 1999 , making Harbin a sub-provincial city .
Simplified: The population of Harbin Municipality is 9,873,743 , 4,754,753 of whom lives in the city proper of Harbin .