John Sievers/Ada A Stevens

My 2nd gret grandparents John Sievers born 1850 Germany and Ada Ann Stevens born 1854 in Michigan were married on 11 October 1877 in Oakland, County, Michigan. I cannot find them on the 1880 Census. Their daughter Lillian (Lillie Ann Sievers) was born 13 September 1883 so they should be on the census somewhere. What is the earliest you can get a birth certificate from Michigan?? I found the marriage record, but where do I order it from? I don't have any more information on John Sievers, so any help would be appreciated. Thanks, Sonseeahray Allen LaPee (Soni)