Unfortunately, your question does not provide enough information to give you a truly meaningful answer, i.e. date and location of death, whether he executed a Will, if there was a surviving spouse, the nature of the promised bequest, etc. In most states, though, you would need to contact the executor or personal representative of the estate for this information. If you don't know who that person is, you could check with the probate court of the county in which your father died to see if probate has been opened in order to determine who you should contact. I would also make sure that the person/person's most likely to have knowledge of this matter have current contact information for you.
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As James stated, more information would result in a more direct answer, but a first step should be to contact any relatives in close contact with your father. They may know whether he had a will. If he did, his executor would be able to tell you if anything was left to you. If he did not, your father would have died 'intestate' which means his assets would be divided accorded to MA law. Depending on whether he left a surviving spouse you may be entitled to a portion of his estate. His estate will need to go through probate in order to effectuate this.
Look through his mail.
Look at his old tax returns.
Ask his friends.
Check with the unclaimed property website.
It is sad but true that very very frequently parents will tell children things that are not true about their estate planning.
Probate (the process of making a will effective) is a public process. You can go to the probate court of the county where he was living when he died and look it up. If there is no record there of his will having been probated, he may have owned all his property jointly or in trust. In that case, you may be out of luck if you do not hear from a trustee.