In the preamble to the Charter for the Town of St. Omer, William Clito, Count of Flanders, states that he has granted this charter because he was petitioned by the citizens, who "have willingly received my petition about the consulate of Flanders, and because they have always been honest and faithful to me."

The principal protection William gives to the people of St. Omer is freedom from tolls, transit taxes, and other charges. This applies to tolls for travel over land ruled by the King of France and Ralph of Peronne, as well as taxes formerly charged by the city administration. It will also include the lands subject to the rule of England and Boulogne, in the event that William makes peace with the King of England and the Count of Boulogne. The houses "in the care of the advocate of the Abbey of St. Bertin" are also made free from toll. In addition, William will prevent the castle guards from collecting private tolls, grant all citizens the protection of his bailiffs, and ensure that debts due to citizens are paid.

William also grants the citizens of St. Omer the use of the pasture in the wood near St. Omer, with the exception of "the land of the lepers." He dedicates the sum of thirty pounds a year, which was due to him from St. Omer, to the repair of damaged property in the town. The charter was signed in 1127, and in the following year, a provision was added for the money which had been in the keeping of the town burgesses to be transferred to the count, and for the town to pay him a perpetual tax of 100 solidi (gold coins) a year.