Mosquitoes have become a problem on your property because it or the surrounding properties have standing water and lots of foliage for them to use to their advantage.
Mosquitoes lay their eggs on top of areas of standing water; any amount from a large pond to water on the top of a tarp can create an issue with mosquitoes on your property.
During the day, mosquitoes like to rest in areas that provide shade from the direct sun. Therefore yards with many trees, tall grass, and landscaping also attract mosquitoes.