"I have a new sod lawn that is about 3 weeks old. Now that it is fall,
my
sprinkler company wants to winterize the system.

My questions are; does my lawn still need to be watered?

If yes, when should the system be winterized? "

First thing I would suggest is that you talk to the company that
installed your sod. They should have told you how/when to water it and
you should follow their directions, so that if there is any problem,
they can't say you didn't follow their instructions.

Clearly at 3 weeks, new sod still needs water, though with declining
temps, the amount needed is decreasing. Whether that comes from
nature or you depends on how much rain you get in the weeks ahead.
You can never tell when it will not rain for an extended period. I
would find out what the latest date your sprinkler company can do your
system, which should still be about a month or so from now. If they
can't accomodate, there are other guys that can blow it out for $50.

If you're worried about it suddenly dropping below freezing, I wouldn't
get too concerned. It would have to go well below 32 for many hours
before the typical system will freeze. And if the temps did drop
before u get it winterized, you could still prevent freezing by just
setting the system to go on for 5 mins per zone every few hours.