The Cook County Clerk's office is the official record keeper for marriages, civil unions and domestic partnerships in Chicago and suburban Cook County. I also swear or affirm that this affidavit is being made for the sole purpose of obtaining the record of marriage for the purpose stated above and that.You have to first obtain a Marriage License and then have a Marriage Ceremony in the City Clerk's Office or a Marriage Ceremony outside the City Clerk's Office. Marriage application must be completed before the couple comes to the office. The Cook County Clerk's office serves as the official record keeper for births, marriages and deaths that occur in Chicago and suburban Cook County.