According to the Great Houses of Serenno, after Serenno led the charge against the Sith Empire in the Battle on Serenno, a planetary government was formed with the planet being named Serenno in honor of the individual who led the charge against the Sith Empire. The planet Serenno and its system then joined the Galactic Republic. The planetary government formed was to be ruled by a Count from one of the six Great Houses in cycles. After a Count was chosen from one of the six Great Houses, a summit was to be requested by the Great Houses in Carannia, the capital city, or in rare occasions, the residence of the Count and the House to discuss the issues at hand. A planetary council was also created that acted as the executive branch of the government and as an advisory board for the Count ruling the Serenno system. The council consisted of the members of the seven Great Houses of Serenno and the Houses that made up the planetary council of the planet and the system were the most wealthy and influential families on the planet Serenno. The council was based in the Great Assembly House inside Carannia and was seen as similar to the Senate. The Serenno military was also created to protect the planet Serenno and its system while individual Houses were protected by their own personal House Guards.
The planetary government formed by Serenno, the individual, was in place for a millennium with the government developing interests in the Gordian Reach and the rest of the Northern Dependencies to establish trade partners. However, over the years since its founding, political ambition and money occasionally led to multiple crisis situations on the planet Serenno. By this time, House Demici and Nalju were the most prominent.
In 106 BBY, the planet was ruled by Count Gora of House Serenno. During his reign, Count Gora began the process of dismantling the Serenno Military established long ago in favor of security droids loyal only to him. Following his lead, many of the other Houses started to dismantle their own House Guards for security droids. Gora then made the decision to lay off workers in favor of droids causing growing unrest amongst the civilian population.
Around 90 BBY, a celebration was hosted in Carannia, the capital city of Serenno to show what the Outer Rim could offer. Under the advisement of the planetary council, Count Gora and his family attended the festival that invited citizens from across the galaxy and the Jedi. It was during this time that Jedi Initiates Dooku and Sifo-Dyas visited Carrania. While exploring the city, Dooku followed then saved Jenza, his supposed sister, from thieves harassing her. After saving Jenza, Dooku went on a tour with Jenza around the city where they visited the Great Assembly House where the planetary council was based. When Dooku touched a carving of the Tirra'Taka, an ancient Serennian legend, a sudden earthquake occurred that caused the destruction of the Great Assembly House.
By 82 BBY, Countess Anya, the wife of Count Gora, died. In 82 BBY, her funeral was held on the moon Mantero that orbited the planet Serenno where Dooku, Lene Kostana and Sifo-Dyas attended the funeral. When Jenza, Anya's daughter, took to the stage to say a speech about her mother, a protest broke out against Count Gora for laying off workers with moon rocks being hurled at Count Gora. Angry about this, Gora ordered his security droids to open fire. Before the droids could open fire, Jedi Padawan Dooku intervened and revealed that he was the son to Count Gora. Even more angered that his Force-sensitive son dared to come back to Serenno and its system, Gora ordered the droids to fire on Dooku. Before the droids could hit Dooku, Dooku came face to face with Gora where they started fighting one another. During the fight, Dooku accidentally opened the coffin of Countess Anya which revealed her dead body. After Jenza shouted to go, Dooku, Kostana, and Sifo-Dyas left Mantero.
By 42 BBY, Count Gora died and was replaced by his son Ramil of House Serenno who ruled the planet. By this time, Ramil orchestrated a plan where he allowed pirates to raid Serenno and its system. With no choice, the other Great Houses began hiring Abyssin mercenaries to protect them. In 42 BBY, Ramil bought out the Abyssin Mercenaries and ordered them to seize control of Serenno and its capital city, Carannia. Lady Jenza then organised a resistance against the mercenaries with Ramil refusing to combat the mercenaries. Outnumbered and outmatched Jenza contacted Jedi Master Dooku who immediately went to Serenno, bringing Lene Kostana and Sifo Dyas. After crash landing in the Delgaldon Plains, the Jedi helped the resistance group take over an Abyssin Outpost near Carannia. Ramil and his droid army then intervened and forced a surrender of the Resistance Group. He ordered Dooku to his ship and told him of how he ordered Abyssin Mercenaries to invade Serenno to help remove the Great Houses thereby removing the infighting that plagued the planet and the system. He then taunted Dooku of how he will kill Jenza using Dooku's own lightsaber. Angered, Dooku summoned the Tirra'Taka which destroyed Ramils droid army. Ramil was killed by Dooku and after losing control of the Tirra'Taka, Dooku killed it. In the aftermath of the battle, a seam of sacanium was uncovered near Carannia.
With Ramil dead, Dooku reclaimed his title as Count of Serenno and became the ruler of the planet with the full support of all the seven Great Houses of Serenno. After Dooku was elected as ruler of the planet and the system, a summit was held at his new residence Castle Serenno to discuss the current issues at the time.
As ruler, Dooku rebuilt Carannia using the seam of sacanium discovered. In 24 BBY, Count Dooku gave the Raxus Address and formed the Confederacy of Independent Systems. He then became the head of the newly formed faction. While serving as head of the Serenno Government. Dooku, like his predecessors, replaced workers and continued dismantling the Serenno Military in favor of droids. In 23 BBY, Count Dooku sent Sith assassin Asajj Ventress to go to Carannia to find her sister who at the time was kidnapped by Glute under the orders of Republic Intelligence Officer Raz Fellidrone disguised as the portmaster of Carannia. After saving Jenza, Dooku came to the apartment that Ventress found Jenza and later ordered to kill Jenza and destroy all evidence. Ventress then proceeded to kill Jenza then cause a fire that destroyed the apartment and the building where the apartment was located.
When Count Dooku, as head of the CIS, based his stronghold on Serenno during the Clone Wars, the world and its system became politically important to the Confederacy of Independent Systems. Serennian dukes such as Duke Solha received prominent positions in the newly created CIS. Although the world became very important, Dooku funded the war effort with a war chest by stealing from his own people as well as exploiting many worlds. In 19 BBY, Count Dooku was killed by Jedi Knight Anakin Skywalker during the Battle on Coruscant.
After the formation of the Galactic Empire, the Empire occupied Serenno and orbitally bombarded at least one city near Castle Serenno. This caused the surving Serennian population from the orbital bombardment of at least one city to go into hiding with individuals such as Romar Adell living in the Upper forest region of the planet. The Empire then occupied Castle Serenno and began shipping Dooku's war chest offworld. In 19 BBY, Clone Force 99 took a mission to Serenno and attempted to steal the war chest however failed to do so.