I am soon to have a child. I want to change my last name to my fathers as I have my mothers maiden name. So I can pass it on to my son.

As an adult you have the right to change your name to whatever you want at any time, as long as it is not for an illicit purpose, such as evading the law.  You file where you currently live. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.