Ohio Wiretapping Law
Ohio's wiretapping law is a "one-party consent" law. Ohio law makes it a crime to intercept or record any "wire, oral, or electronic communication" unless one party to the conversation consents. Ohio Rev. Code § 2933.52. Thus, if you operate in Ohio, you may record a conversation or phone call if you are a party to the conversation or you get permission from one party to the conversation in advance. That said, if you intend to record conversations involving people located in more than one state, you should play it safe and get the consent of all parties.
Additionally, consent is not required for oral communications (e.g., in-person conversations) where the speakers does not have a reasonable expectation of privacy in the communication.
See Ohio Rev. Code § 2933.51. This means that you are free to record a conversation happening between two people in a public place such as a street or a restaurant, so long as you are not using sensitive recording equipment to pick up what you otherwise would not hear.
In addition to subjecting you to criminal prosecution, violating the Ohio wiretapping law can expose you to a civil lawsuit for damages by an injured party.
Consult the Reporters Committee for Freedom of the Press's Can We Tape?: Ohio for more information on Ohio wiretapping law.