On August 12-year 1991, the 9th session National Assembly term VIII issued a resolution to divide Ha Son Binh province to re-establish Ha Tay and Hoa Binh. At the same time, return Son Tay town and 5 districts: Dan Phuong, Hoai Duc, Ba Vi, Phuc Tho, Thach That of Hanoi city to Ha Tay province.
From August 1 year 2008, the entire area and population of province Ha Tay was merged into Hanoi City. From there, officially dissolved Ha Tay province. On May 8-year 2009, Ha Dong city became Ha Dong district under the capital Hanoi, Son Tay city became Son Tay town under the capital city of Hanoi. At the same time, the boundaries of Quoc Oai and Thach That districts were also adjusted and merged with four more communes in the district Luong Son, province Hoa Binh.