If there was a need to file his Will, you should have received notice. Lack of notice to you would indicate that Dad used a living Trust or other non-probate methoda to pass his assets at death.
You should be able to access online the county Probate Court's Index to see if a case was ever opened. It might not be called the Probate Court, it could be titled differently, like surrogate, family, superior . . .Ask a similar question