The town is an old sea lock and already in the 16th century formed the mouth of the Steenwijker Aa ( river). Especially the peat, which was won in the hinterland, caused much activity. Johan de Ligny, Count of Aremberg, Stadtholder of Friesland, Groningen, Drenthe and Overijssel, may be mentioned as major stimulator of this environment. He created and improved access canals for the trade.
During the Eighty Years War the city was strengthened (in 1581) by Sonoy of Diederich, this way it became an important focal point on the east side of the Zuiderzee ( which is now "new land" and IJsselmeer) for the States fleet and a base for the troops against the Spaniards.
The name Blokzijl, (meaning reinforced lock) was then created. Blokzijl was a long time under Spanish rule and in that time prosperous and rich. The town lay on the Zuiderzee and was an important trading point. Blokzijl gained city rights in 1672.
Today it is a tourist town; Blokzijl has its own harbor for pleasure boats and a lock. Larger tour boats make regularly a stopover at Blokzijl . On the quay is an old cannon, where tourists like to take a photo of each other.