I imagine the PCs as having grown up in the town, living a hard life helping defend it, showing a knack for weapons and magic, and slowly yearning for more outside the village.
Things your character may want as a background
Family history: Your family may have an important role in the town, either being farmers, important landowners, previously being blacksmiths, etc. This may also help give your character a goal of something important to build up in the town, such as a blacksmith's son being driven to open the local mine again, drumming up work such as contracting weapons for the growing town militia and caravan guards, and finally bringing dwarven weaponsmiths to town under the same blacksmith company.
Character goals for the town: Your character may have a driving goal for the town. A PC growing up as a farmer may just want it safe and plan to live there for his entire life. They will drive toward having town guards, clearing the area, building a defensible wall, and forging allies nearby. A PC growing up from a rich family may want to forge trade alliances with nearby towns, will clear the trade routes, and want this town to return as a central trade position, with his family acting as negotiators and landholders, growing rich during this time. A PC who lost a lot of family in the war may concentrate on defeating the subhumans, treating the town as a base of operations that needs to be secured, so that other towns can be secured, so that eventually humans have a safe area from which they can strike back and make the entire continent safe.
Dragonborn: Dragonborn are not native to town, but some are residing in it, left stranded as caravan guards when trade stopped, or travelers who have reached here but find it hard to move on due to the danger. The Dragonborn as a race have been rare lately. There is little honor and battle when an army of goblins sneak into your town at night to steal your food, and most seem to have moved on to remote areas.
Dwarves: Most Dwarves live far north, in the cold mountains, but some could be living in the city. The area used to be a major trade hub, and attracted dwarven jewelers and blacksmiths to support that, especially given the dwarven shipments that came down the river. Dwarves as a race have withdrawn to their mountain fortresses, often defending themselves from subhumans boiling up from tunnels into the Underdark.
Eladrin: Eladrin are rarely seen, seemingly withdrawing with the forests as the swamps took them over. Stories are told of a large encampment that used to be in the center of the forest near town, but no contact has been made in decades.
Elves: Most Elves seem to have disappeared far to the West, past the swamplands, to their great forests.
Halfling: The home of the Halflings is in the vale to the north. Many travelled through the town while trade happened, tagging along to caravans or selling produce. The Vale to the North was once a huge land of rolling hills, verdant plains, and peaceful villages. It seems that the Halfling's legendary luck held true, given that their lands are mostly surrounded by many other races, preventing open war from coming to them, but most still spend the bulk of their days hiding underground in their holes.
Tiefling: Once a common sight travelling through town or seeking out magical ingredients, their caravans are a very rare sight these days. They live on the road in roaming caravans, though there are always rumors of dark strongholds still running, where many originally got their demonic powers and still deal with demons to this day.
Cleric: Many townsfolk whisper a prayer to many gods, given the danger and darkness currently around them. The temple must currently service everyone in town, given the lack of one strong group of worship. Your healing skills have helped the town protectors.
Fighter: You've likely learned to swing a blade getting ready for kobolds raiding the town and farms, or might have come to town as a caravan guard and gotten stranded there.
Ranger: While there is danger outside of town, there is also valuable prey to hunt and monsters to run off.