Ah, a subject near and dear to my heart. I'm an Illinois resident and I go for walks with a neighbor year round. We are out there walking for exercise, not taking a stroll, and I assume that is the case for you as well. Because we are never standing still in the cold I've found that a lightly insulated hiking style boot works the best. Something with 200g - 400g of insulation should do if you wear a good wool sock with it. I have a pair of Merrill's that don't look like winter boots, but they fit me really well so they are comfortable to walk in and they have just enough insulation to keep my toes warm as long as I keep moving. Tip - for my bell-ringing shifts, I use toe warmers which are like hand warmers, and they last 2 hours.
Moving up the body, I bought a pair of flannel lined jeans last year and they're pretty comfy. On really cold days, long johns are still the way to go. My main weapon against the cold is a down parka. I've tried the layer approach, but I am tall, and the shells for most layering systems are not long enough for me. I wanted something that covered my butt and I finally found what I was looking for in the Mountain Hardware Downtown Coat. I can still use layers to adjust for conditions; often I'll wear the parka with only a heavy synthetic long sleeved t-shirt. On a really cold January night I'll add an additional insulation layer.
As others have posted a scarf or neck gaiter is a necessity particularly when the wind is blowing. I have both, but I think a nice comfy scarf is a little more flexible for taking a walk. I like Patagonia's Micro-D (for Delux) scarf. Long, unbelievably soft, and machine washable. For head gear you should own at least one hat that is advertised as being wind proof. When it comes to keeping my fingers warm, I struggled until I bought the Downtown Coat. It has long sleeves with stretchy cuffs inside and once I finagle them over my gloves, they seal out the air pretty well and now my hands stay pretty warm. I am keeping my eyes open for a pair of really good mittens, but they don't seem to last long enough to make it through to the post-winter sales.
Unfortunately, none of this stuff is cheap to buy right now and you apparently only need it for one season. Can you "mall walk" on the really cold days to avoid investing in cold weather gear?