First, how old are they? Many people think that chickens start laying at 20 weeks old, but in reality, it can vary from 5-7 months. Anything within that time frame, and even outside of it, is still a normal age for egg laying.
Is there any place that they could be hiding eggs? Do they free range? Sometimes, it will look like birds aren't laying, but one day, you'll find a stash of eggs in a random place.
Because daylight hours (at least in the United States) are decreasing, it is possible that yours won't start laying until spring. Ideally, chickens need at least 14 hours of daylight for maxiumum production. But, if yours are pullets that haven't laid before, they'll likely lay through the winter despite the short hours.
Lastly, are you sure that they are all hens?