What % will I be penalized for cashing out 401K?

My dad died in 2006. I recently learned of a 401K that he had taken out and I am sole beneficiary. I'm not sur of the amount, because the company said they can't tell me, of course, until they verify who I am and receive my information. I've been told by a close friend of my dad that it is around $20,000.00. I am 22 years old, about to start college, and have a family. I've heard that income can play in to how much you are penalized. I'm not sure of that applies to me, as it's not "MY" 401K. Anyways, I do not work. My husband does. I am a stay at home mom. He makes $30,000.00 a year. I don't know if this info helped, but I was just curious. Thanks!