A dark closet next to an exterior wall could be a moldy place. A furnace cabinet or bathroom that is without proper ventilation could be a source of mold as well.
The pipes of an air conditioner and drip pans may be a place where mold could grow.
Sweaty shirts, wet towels and even shoes after a workout may have the potential of bringing mold into a house.
Areas that have a lot of steam in or around them, such as showers, humidifiers and cooking areas, are all subject to mold issues.
Some places that have poor irrigation or lots of shade that does not allow a watery spot to dry could allow mold to form.
Leaky toilets, dishwashers or bathtubs all are places where wet spots and therefore mold might be found.