This is a paid asset, but now you can download Low poly downtown kit Free.
Detail this asset from Unity Store: Original Link
Low poly downtown kit v1.0 (Latest version)
“If possible, please buy the package to support the developer”
This is low poly down town kit. It contains modular roads, modular trees, gas stations, police station,train station, living private houses, dormitory houses, business buildings, fences, street props, garden props,graphics profile for post processing stack and demo scene. With this kit you will be able to create rich environment with amazing graphics.All models unwrapped in to low res textures, optimized and prepared as prefabs. Buildings colors can be changed by swapping textures from “palettes” folder.