Find 1 studio apartments for rent in O'Fallon, IL. A studio apartment is an open-concept unit that combines the living area, bedroom, and kitchen into one room, with only bathrooms and closets separated by walls. Studios are typically less expensive than traditional apartments and take less energy to heat and cool. Many studios offer full kitchens, providing essential utilities in a compact, efficient space. If you opt for an efficiency apartment, your kitchen will be more compact with fewer full-sized appliances, but you will enjoy more living space.