Marriage records are important for verifying and confirming relationships. In Williams Co., OH the records can be found at the Williams County Records Center and the Bowling Green archives.
The records at the Center run from 1824 to 1984. This is again the place to obtain records that are certified. It is wonderful that the records reaching such a early date.
The Archives in Bowling Green has the marriage records from 1824 to 1941. They also have a index of the marriage records, but only from 1824-1868.
Be certain when checking marriage records for the witnesses on the document. They often can provide valuable clues of marriages and related surnames.
Good luck in your marriage hunt.