Original: After Sirius' death later in the series, all of his remaining possessions are also passed along to Harry, including Number Twelve, Grimmauld Place.
Simplified: After Sirius' death, all of his remaining possessions were passed along to Harry. This included the Black family residence, located at Number Twelve Grimmauld Place, and all the contents and furnishings of the house, including Kreacher (the old Black family House Elf).