The Black Keirgo slums are named after Keirgo of Anequina. In 2E 309, Keirgo of Anequina and Eshita of Pelletine would come together and united the two nations to form the Elsweyr Confederacy. Although it isn't mention, it is likely that the Black Keirgo slums were named after Keirgo himself.
When the city of Senchal was inflicted by the Knahaten Flu, Senchal was in a state of chaos. Neighborhoods were razed by the mad effort of cleansing the city of the illness and have yet to be rebuilt. The Knahaten Flu originated in the Black Keirgo slums, more specifically in Sweet Street. The flu was seen on the Skooma-struck citizens. The flu eventually spread further into Senchal, then to Alabaster, then to the rest of the Elsweyr cities.