1) On Using the "Ohio County Marriages, 1789-1994" Collection on FamilySearch (posted 10 October 2013):
a) Nancy said: "It's interesting that marriages were recorded for Ohio counties in 1789 because Ohio wasn't a state until 1803. Until then that it was part of the Northwest Territory. I suppose marriages in that wild country happened and had to be recorded somewhere."
My comment: The Northwest Territory was probably the administrative entity before statehood, and there may have been several "counties" that kept records. Or they collected records after statehood.
b) T suggested: "You might find something here, too. http://madisonoh.ancestralsites.com/marriages/b.php"
My comment: Thanks for the suggestion.
c) bgwiehle helped: "1. This database has been available since at least Apr 2011 [as "Ohio, County Marriages, 1790-1950"]. It is frequently updated with additional index entries and images.
2. Because of the way FamilySearch has set up the records, each person indexed will have their own page. Depending on the entry and the indexer, there may be pages generated for six persons - bride, groom, and each of the parents.
3. Generally there is only 1 image per record for this database, but one should always check the previous and subsequent images, just in case. Also, some of the early records are organized in alphabetical Bride's and Groom's lists, so there are duplicate entries for each of those marriages.
4. There are still gaps in the coverage. Follow the "Browse through 2,648,655 images" link (on the database search page) to access the waypoints, which have descriptive titles (eg. Crawford County, Marriage records 1850-1854 vol 4). See http://www.genealogybranches.com/ohio.html for alternative databases and websites.