Tradition states that the Craft flourished in Belgium at Mons as early as 1721 but the first authentic Lodge, Unity, existed at Brussels in 1757 and continued work until 1794. A Provincial Grand Master Francis B.J. Dumont, the Marquis de Sages, was appointed by the Moderns Grand Lodge in 1769. For some years, however, opposition from the Emperor hiudered the expansion of the Craft.
0n January 1, 1814, there were only 27 Lodges in existence in the country.
A Grand Lodge was established by Dutch and Belgian Brethren on June 24, 1817, but it was not successful. Belgium became independent in 1830 and a Grand Orient was formed on May 23, 1833, out of the old Grand Lodge. In 1914 it controlled 24 Lodges in Belgium and one in the Belgian Congo.
King Leopold was himself initiated in 1813 and, although he never took a very active part in the work he always maintained a friendly attitude towards the Craft.
On March 1, 1817, a Supreme Council of the Ancient and Accepted Scottish Rite was established.
the source: Mackey’s Encyclopedia of Freemasonry