Dacheng County is subordinate to Langfang City, Hebei Province. It is located in the east of the middle of Hebei Province, the southernmost tip of Langfang City, adjacent to Jinghai District of Tianjin City and Qingxian County of Hebei Province in the east, Wen'an County in the north, Renqiu City in the west, and Hejian City in the south. The total area is 904 square kilometers. The total population is 530000, with Han people accounting for the majority. By 2020, Dacheng County has 10 towns under its jurisdiction.

In the fifth year of Emperor Gaodi of the Han Dynasty (202 BC), it was set in Dongpingshu County, which belongs to Youzhou Bohai County. In 1989, Langfang was renamed Langfang City, and Dacheng County was subordinate to Langfang City.

In 2020, the GDP of Dacheng County will be 17.6 billion yuan, with an average annual growth of 6%. The ratio of the three industrial structures is 10.5:44.5:45.