Haiyan, a county of Zhejiang, is one of the birthplaces of Majiabang Culture, Songze Culture and Liangzhu Culture. Established in 222 BC, i.e. the 25th year of the reign of Emperor Qin Shi Huang (247 BC -210 BC), Haiyan derived its name for its rich coastal areas and salt fields (“hai” in Chinese means “sea”, and “yan” means “salt”). Since its founding, it has relocated its county seat four times and undergone six territorial divisions. At the end of the Qin Dynasty (221 BC - 207 BC), the county seat sank to become Zhahu Lake, so it was moved to Wuyuan (east part of today’s Pinghu City). From the year 126 to the year 131, the county seat sank into Danghu Lake, so it was relocated southward near Guyi Mountain of Qijing (near present-day Zhapu Town). From the year 200 to the year 203, the southwestern part of Haiyan and the southern part of Youquan were separated from Haiyan to establish Haichang County (Haining City today). In the year 341, the county seat was moved to Mahao City (southeast of today’s county seat of Haiyan), and in 507, the northeastern part of Haiyan was established independently as Qianjing County; from the year 534 to the year 535, the northeast part of Haiyan was established as Xupu County. In the year 717, the county seat was moved to current location in the Tang Dynasty (618-907). In the year 751, the northern part of Haiyan, eastern part of Jiaxing, and southern part of Kunshan were combined to establish Huating County. Haiyan was elevated to a prefecture-level city in 1295, but reverted to a county in 1369. In 1430, Haiyan’s four towns Wuyuan, Qijing, Huating and Dayi were combined to establish Pinghu County. Haiyan was liberated on May 7, 1949. In May 1950, three villages of Shiling Town were transferred to Haining County, while ten villages from Pinghu County were incorporated into Haiyan. On November 21, 1958, Haiyan County was merged into Haining County, and its Xitang, Haitang and Yuantong were transferred to Pinghu County. Haiyan County was reestablished on December 15, 1961, comprising two towns and sixteen gongshe (gongshe is similar to a town), but Shiling Gongshe remained under Haining County. In 1983, the gongshe was replaced by the town. In August 1985, Ganpu, Tongyuan and Xitangqiao were upgraded to towns, and so did Yucheng, Baibu, Changchuanba, and Shiquan later, and Changchuanba was later renamed as Qinshan.

In January 1999, Futing was abolished and merged into Wuyuan Town; in November this year, Chengxi, Qijia, Liuli, and Guantang were dissolved and incorporated into Wuyuan, Shendang, Ganpu and Qinshan respectively. By the end of 1999, the county comprised 12 towns: Wuyuan, Shendang, Ganpu, Qinshan, Tongyuan, Xitangqiao, Yucheng, Baibu, Shiquan, Haitang, Yuantong and Henggang. In October 2001, Haiyan’s administrative divisions were readjusted, consisting eight towns: Wuyuan, Shendang, Ganpu, Qinshan, Tongyuan, Xitangqiao, Yucheng and Baibu. In 2010, those towns were integrated into four sub-districts: Wuyuan, Xitangqiao, Yuantong and Qinshan, and five towns: Shendang, Baibu, Yucheng, Ganpu and Tongyuan. In September 2018, Yuantong Town was replaced by Wanghai Sub-district, and now the county has four sub-districts (Wuyuan, Qinshan, Wanghai and Xitangqiao) and five towns (Shendang, Baibu, Yucheng, Ganpu and Tongyuan) under its jurisdiction.