This year mosquito populations have been relatively high because of the increased rainfall and warm September/October. Populations of all species will decline once temperatures fall low enough.
They get in around and under doors that do not seal, via pet doors, and windows if they are open and screens are not intact. There are a number of species that once inside will actually utilize the water reservoirs indoors to lay eggs in and relatively large numbers of mosquitoes can begin showing up indoors. Places to look for developing larvae include: flower vases, sink overflow and P-traps (the u bend pipe under sinks), evaporative cooler condensate trays, toilet cisterns, any indoor water features. It’s a good idea to check around your home for larvae also.
In our lab (where we rear mosquitoes) we use an electrocution mosquito swatter to take out any indoor escapees (I also have one at home to eliminate any that get inside.
We have a lot of information that you might find useful (see links below).