William Jackson Brack (June 17, 1837 – April 30, 1901) was the first mayor of Orlando, Florida from 1875 to 1877.

He married firstly to the former Olive Chancey (1838–1864) of Clinch County, Georgia, by whom he had two sons who died young.

He was certainly there by October 16, 1873, when he was mentioned as guardian ad litem for the orphans of Mrs. Lucinda Hughey Terrell in a lawsuit filed in the circuit court of Orange County, Florida.

After leaving office, the former mayor remained in the Orlando area as a farmer and fruit grower until at least 1880.

From that point, he also captained a 35-foot sidewheel steamboat called "Spray" along the inland canals that connected the Kissimmee River valley to Fort Myers, Florida on the Gulf of Mexico.