I also live in northern Minnesota. I have 10 hens, 7 months old, and usually get between 6-8 eggs per day. For the wife and me, that's more than we need. I don't use any lights to lengthen the day, and encourage more egg laying, because I get enough eggs as is.
I have 10 different breeds in my small backyard flock of 10 hens. And I can not say for sure which of my brown egg layers is always laying eggs. What breed(s) of chickens are in your flock? I selected a number of breeds that were noted to lay eggs in winter. But not all breeds are as good as others.
What are you feeding them? Do they get enough? My chickens are eating their feed like crazy - about 1.5 times more than summer consumption. But I read that is to be expected. I have feed in a hanging feeder 24/7 for my girls and never let it run out. Fresh water is available in a 3 gallon metal fount sitting on top of a metal base heater. Food and water is always basic to good health.
Stress on the chickens can cause problems with egg production. Is your coop draft free and well ventilated? Is your coop big enough for chickens in winter in Minnesota? My girls have no desire to go outside most days with all the snow on the ground, and spend almost all their time in the coop. I anticipated this and built my coop almost twice the recommended size for my 10 hens. I think that helps keep the stress down as the girls don't feel cramped in a small coop.
December 22 will be the shortest daylight hours of our year, and after that the daylight hours start to get longer. So maybe we are almost through the least productive time for egg laying - at least in terms of hours of light per day. However, I usually see our coldest days in January and February, so it will be interesting to see if egg production increases or decreases during that period.
Hope you can get your egg production back on track. Best wishes.