For canon information, see the Mass Effect wikia page for Eden Prime.
One of the first human colonies established beyond the Charon Relay, the agrarian colony of Eden Prime is described in such words as 'idyllic'. Due to its fertility and uncanny suitability for Earth life, the colony attracted heavy immigration, becoming one of the Alliance's larger colonies, with a population of roughly 4.2 million before the Reaper War.
Prior to the war, Eden Prime launched a major project to restore the ecosystem of one of the settlement's major lakes following the release of Skald Fish.
Established in 2152, Eden Prime enjoyed heavy investment by both the Systems Alliance government and private interests. The planet quickly became the symbol of what an extraterrestial colony could become, with space-efficient arcologies towering above vast fields of various crops and an extensive monorail system. While celebrated, it was generally considered a backwater posting for the Marines and sailors stationed there in its defence.
That all changed in 2183, when the colony was attacked by the geth, sparking the Eden Prime War. Whole Marine units were decimated in the attack, and despite a swift counterattack by Alliance forces, the planet was the first to witness the horrors of husking - as a result of this, its settlements were focal points of the battle, reducing some arcologies to rubble.
Rebuilding efforts were not completed at the time of the Reaper War, and while the colony was never occupied by the Reapers, it was again attacked by Cerberus forces. This time, there were no Alliance rescuers to mount a counterattack. Facing a war on two fronts, the Systems Alliance restricted its aid to intelligence and supply assistance after its garrisons on the planet were overrun by the enemy. Despite this, the Eden Prime Resistance successfully forced Cerberus to withdraw from the planet, restoring supply lines to Alliance forces.
After the Reaper War, the colony has seen an influx of immigration from Earth and the Illuminated Primacy (migrants from the latter being drawn by Prothean infrastructure discovered there during the war). A combination of pride in the Eden Prime Resistance, anti-immigration sentiment, resentment at the Alliance's failure to aid the colony during the Cerberus attack, and the time spent cut off from the Alliance military government has resulted in some currents of proto-nationalism amongst the population, leading to tension with the Marine garrison.
- Constant: the capital city of Eden Prime. The largest settlement and the epicenter of the monorail network, it's home to the factories, plants and silos that process or store Eden Prime's produce before it's shipped off-world. Situated in a temperate, green region on the planet, it's generally considered one of the most beautiful cities in Alliance space. Home to the pre-war colonial administration and a large Alliance base (currently garrisoned by the 2/4th Marine Battalion amongst other units), it has seen the worst of the tensions between pro and anti secessionists, including a riot in which several Marines were injured and colonists arrested.
According to J proctor (Janice Proctor):
"The home of pastoral farmers, hippies and land labourers. Big on heart, low on brains. Has a population of almost four million people, but only four family names to go between them. Like most colonists, Eden Primers vehemently asserted their independence, until the geth tore them a new asshole and they had to be bailed out by the Alliance. Their economy consists entirely of agricultural exports and Shepard memorabilia. Like Iowa spread over a planet, and exactly as horrible as that sounds."