Other than the Family History Library in Salt Lake City, the Wilmette Family History Center is THE place to go to research early Chicago and Cook County vital records.
They have complete collections of births to 1915, marriages to 1916, and deaths to 1947 on microfilm and anyone can use the films free of charge.
What they don't have is all of the available films for births 1916-1922, marriages 1917-1920, and Cook County deaths outside the city of Chicago up through 1947, and when FamilySearch stops circulating films on 31 August 2017, they will no longer have a way to add to their collection.
Last count, Wilmette needed about 600 films to complete their vital records sets and the good news is FamilySearch appears to be running a sale on extended loan films. For $7.50 (1/3 the normal price) one of those films can now be added to the collection.
If you live within driving distance of Wilmette and research Chicago families, it would be to your benefit to help complete the collection before it's too late.
If you live hundreds of miles away from Wilmette, there might not be a direct benefit, but there is something to be said about being part of a group that accomplishes something for the good of many and $7.50 is a small price to pay for that.
If you are interested in helping the Family History Center collect the remaining films, contact them in one of the ways below and tell them ChicagoGenealogy sent you. :)
Wilmette Family History Center