If you want to count on seeing bicyclists in Chicago, regardless of the weather, I recommend Milwaukee Avenue, anywhere between Logan Square and the Loop. During one one-mile ride, I counted more than one hundred cyclists heading in the opposite direction. On warm summer days, you would be sure to see more on the lakefront path, but on Milwaukee, you will see dedicated, life-altered commuters.
How does one encourage bicycling? Of course, through design -- of roads, signage, lighting, and land use. The environment, at every scale, can discourage or encourage cycling. A second factor, which is more difficult to quantify or control, is through changing cultural attitudes. Attitude may be why Milwaukee Avenue is such a cycling thoroughfare. It connects neighborhoods with large young populations, usually more open to trying new or "forbidden" things.