This question has dogged me, as I purchased my own home in 2010 but around 2012 began to stay more with my elderly folks for reasons regarding illness/need (mine and theirs). I always regarded my own home as my primary residence but now (for tax purposes) wonder about that.
“A legal residence, also known as a domicile, is the place you consider your permanent home. It's the state you intend to return to after a temporary absence.
A person's legal residence is important for legal purposes, such as: Determining jurisdiction or choice of law, Determining a person's tax status…”