How many years married before a spouse is entitled to pension in Ohio?

Not enough information is given in order to answer.

Entitled to the spouse's pension under what circumstances? Death? Divorce? Sham marriage? Common-law marriage?

Not only is more information needed, all pension benefits are going to be different depending on the type of pension it is (e.g.: union pension - private employer pension - government pension - military pension?)

You should probably consult with legal counsel over this question as it can get quite

complicated depending on the circumstances, just a few of which are enumerated above.