In the late Stone Age, Ninghai was already home to primitive settlements. In 280 AD (during the West
Jin dynasty) it was recognized as a county, whose seat was at Baijiao. Later, during the
Sui dynasty (589 AD), it ceased to be an independent county and instead became part of the
Linhai County. The year 621 AD saw it restored as a county, with its seat at Haiyou (part of the present
Sanmen County), subsequently merged into the Zhang’an County. In 689 AD, as Empress
Wu Zetian rose to power, Ninghai's administrative status was once more restored to county level, with its seat placed at Guangduli (the present
Chengguan Town). During the year 706 AD, the eastern land expanse of the county was put under the jurisdiction of the
Xiangshan county. In 1940, i.e. the 29th year of the Minguo period, a new county, Sanmen, was established. It comprised 17 towns, including the town of Haiyou. After its establishment as a county, Ninghai had successively been part of Linhai Prefecture, of the Taizhoulu Prefecture, and of the Taizhou Prefecture. When the PRC was founded in 1949, the county land was first part of the Taizhou Prefecture, then became part of the Ningbo Prefecture before it reverted to the Taizhou Prefecture. But in October 1958, it was abolished as an independent county and was incorporated into the Xiangshan county, whose seat was successively the towns of Liyang and Chengguan. In October 1961, Ninghai county was re-established as part of the Ningbo Prefecture, of which became Ningbo City in July 1983. ==Administrative divisions==