The 2008 Ohio Democratic presidential primary took place on March 4, 2008 and was open to anyone requesting a Democratic party ballot. In 2008, any registered Ohio voter could on election day request a primary ballot of either the Democratic or Republican party, by signing an affidavit stating that they supported the principles of the party whose ballot they are obtaining.

The 2016 Ohio Democratic presidential primary took place on March 15 in the U.S. state of Ohio as one of the Democratic Party's primaries prior to the 2016 presidential election.