Wikipedia says pumpkins are a warm season crop and in the US most grow
in Illinois and are planted in July.

http://en.wikipedia.org/wiki/Pumpkin

Now obviously the US is a big place and has different climates in the
north and south but in my experience pumpkins need a long growing
season to allow the fruit to reach full size and to ripen. Here they
grow between last frost and first frost, about 8 months, even so a
number are not full size or ripe as the vine keeps flowering and
setting fruit up until death. I grow table (not cattle) pumpkins and
in that time I get about 30 mature fruit (100kg, 250lbs) per vine. The
vine is quite large!

If it is too cold to plant until July how long can the season be, two
or three months? Does this mean that each vine only ripens the first
set fruit in the limited time? What kind of yield per vine do they
get?

Could somebody with relevant experience who is not too far from
Illinois shed some light please.

David