Simba City is a large African conurbation covering all of Equitorial Guinea and extending south into former Gabon and north into Cameroon. The city is part of the Hiroshima Accord. Elaborate buildings on the coast resemble vast animal ribs.
The Simba City Territories cover Gabon, southern Cameroon, the Republic of the Congo, and part of the Democratic Republic of the Congo. Its land is outside of Pan-African Judge jurisdiction.
The main airport is the Yondo Black Memorial Hoverport.
Simba City was part of the Credit Wars, when the African nations refused to pay their crippling debts and ended up at war with the Western powers.
The city joined Luna-1's "Global Lunar Partnership Treaty", agreeing to guarantee the neutrality of Luna-1 and provide Judicial assistance. In reality it hoped, like all Treaty members, to have influence in the lucrative colony.
As with the rest of the Earth, Simba City fought off a zombie invasion during Judgement Day.
In 2115, conditions in the Great African Dustbowl led to famine in Simba City. A resident attempted to enter Mega-City One by clinging on to a plane (Dredd sent him back). In the same year, Devlin Waugh visited the city and was stalked by a deranged fan.
The African continent was ravaged in 2117 by the returning Yoruba pantheon. Simba Territory armed units assisted the Pan-African Judges in a futile attempt to destroy the gods Esu and Shango. After the armed forces were routed, the Simba City Territories were among the lands devastated in retaliation. 
Judge Dredd visited the city in 2119, tracking down the sorceror Kigishu; Simba City at the time was wracked by its second great famine of the year, with further townships collapsing entirely, and the Simbas allowed his unofficial visit in exchange for more aid. He worked alongside Field Judge Shaka, the best guide in the Congo Basin-Rift Valley badlands. Simba City at the time had a midnight curfew. 
In 2126, Simba City was one of multiple states that stepped back and allowed the Sov Block to violate Luna-1's sovereignty. Ironically it was a Simba City transplant, Tek-Judge J'aele, who helped defeat the invasion and allow acting-Marshal Dredd to annul the Partnership Treaty so Simba lost all control. J'aele remained on Luna-1. 
Simba City is a judicial dictatorship, with a Judge force separate to the Pan-African one. At some point in the 22nd century and ending in 2126, it sent Judges to Luna-1 (sometimes ones that had annoyed someone or screwed up at home).
When shown in Darkside (and described in Eclipse), the Judges had blue uniforms with no helmet, a thin earpiece/mike headset for communications, a striped animal-skin pattern right-shoulder pad, and a cheetah-skin patterned gun holster. In Fetish, set roughly the same time, Judges had a white uniform with stylised, gold/bronze lion-head shoulder pads, a black lion emblem on the chest, and a golden headcap.
Subdivisions included Tek-Judges and Field Judges. The latter used Voortrekker-series 9000 lev-sleds.
Field Judge Shaka had been born and raised in the jungle before he joined the Judges, and told Dredd this wasn't too unusual.
"Dredd's World" in Judge Dredd Mega Special #1 introduced the idea of a coastal west African megacity; prog 701 followed this up and named it Simba City. The "Dredd's World" city was much bigger, covering the coasts of Nigeria, Benin, Togo, Ghana, Cote D'Ivorie, and Liberia.
The Pan-African world map in the Megazine said Simba City was the "closest thing Africa has to a Meg (outside Luxor)". As Simba City is shown to be quite large, it's not clear what keeps it from being a megacity.
Yondo Black was a Cameroon lawyer arrested in 1990 for trying to create a political party. (He later ran for president)
In "I Hate Christmas", a stowaway from Simba City says he's escaping conditions in the Dustbowl - which is quite far from Simba.