Answer: Many things will be different by December. Some of these things are predictable, others are not. For example, we know that by next December you will have a little over a full year of practice experience behind you and that you will be considered a second-year associate. What we cannot know is what the employment market will be like in Chicago for second-year associates in your particular practice area (which you did not disclose to us).
There are also certain factors about your background that we do not know and because you did not tell us, I cannot fully advise you. Here are some of the facts that prevent us from knowing the full picture: where you went to law school, how you did there in terms of your grades and class ranking, your current practice area, and how well you are doing at your current firm. All of these facts will contribute to your success or failure in your job search.
I am willing to take a guess on some of these unanswered questions simply based on the fact that you are working at a large regional firm with, as you have told us, an excellent reputation. My guess is that you either went to a top rated national law school or, at the very least, one of the top regional law schools and your grades were quite decent at the very worst.
Based on this supposition, and still without knowing your practice area, let's fast forward to a Chicago job search. If you went to a top ten national law school, you should be a viable candidate as long as your practice area is flourishing. However, if you went to a regional school, your viability diminishes in comparison to your competition that may have attended University of Chicago or some of the well-regarded regional law schools in the Chicago area.
Then if you factor in a practice area that is not in demand, you will find that you job search will be less than fast track.
Now let's throw in a major unknown: the economy. Based on predictions along with obvious observations, the economy is certainly slowing down. How will that affect the attorney job market in Chicago over the next ten months? That is anybody's guess, but what if there truly is a dramatic slowdown? What if the only opportunities available to you at the time of your job search are those in the major law firms? Are you going to hold out for a "less stressful" environment or will you need to go to work shortly after you make the move to Chicago? And by the way, if you decide to make the move without having a job lined up, it will be that much harder to find a new employer.
One more item to add to the list: as a second-year associate, there may not be as many opportunities available to you as you might be thinking. Depending on the economy, there should be a fair amount of open job requisitions by the spring for second-year associates but then again, the question comes up as to how long you can be unemployed (and each day that you are unemployed makes your job search that more difficult).
So, here is what I am getting at. Before you close the door to the large firms, wait until you see what the job market for your practice area, years of experience and credentials in Chicago are like later in the year. Which leads me to the second part of your question as to when you should start your job search.
If you are moving to Chicago in December, that generally means that you will be starting your new job right after New Year's Day. I would suggest that you start your search in September or, at the very latest in the early part of October for a projected January start date. You certainly do not want to wait until November when we are getting into the holiday season.
All of this is based on the assumption that you are willing to take some time off from your job to spend a week to ten days in Chicago for the interviewing process. You need to let prospective employers (or your recruiter) know that you are currently employed and that you would like to have your new job tied down before you move to Chicago in December. Therefore, it would be preferable to have screening interviews scheduled with a tentative time and date for advanced interviews for that same week (or even the same day) if there is mutual interest. Pick a definite week that you plan to be in Chicago and let the firms know the date as early as possible.
The bottom line: before you determine that you are not going to interview with the large firms in Chicago, understand that you would be well served to keep an open mind so far in advance of your moving date. You are a very junior attorney and may not be able to pick and choose the kind of lifestyle you want at this stage when you couple that desire with a geographical move and perhaps not the most viable credentials or economic conditions for the Chicago market.
The good news is this might be moot if the economy heats up again and junior lawyers in just about every practice area are in high demand. Just hold up from making any hard and firm decisions until it gets closer to the time when you should begin your search.
Summary: Planning on making a move to another law firm requires careful planning and thought before making your move. Learn how far ahead to plan when making a move.