Am I considered Jewish if...?

My grandma came from a family of 13 kids. They were all raised Orthodox Jewish, and came from a long family tree of Judaism. But, my grandma was one of the youngest in her huge family and was very young when her Dad died. After he died, her Mom had all the kids work to help make ends meet. Her Dad was no longer there to take the kids to temple and everyone had to work, so my grandma never practiced Judaism. She never denounced her Judaism, but just never practiced. My grandma married a Jewish man, who also was not active in Judaism. Hence, my Dad didn't practice Judaism. My Dad married my Mom (who has no Jewish background in her family tree). I've heard that even if my Dad's side is Jewish, since my Mom isn't, I'm not considered even part Jewish, because Judaism is ped through the woman. Is that true? I'd love to learn more about my roots. Thanks! :)