Beyonce is a decent singer, and nothing more. She is neither enlightened enough nor renowned enough to become a member of the fabled Illuminati. Even if this group really exists, only the most elite members of society would be invited to belong. Beyonce just doesn't have that level of greatness.
The REAL Illuminati is an organisation that controls the worlds finances. The Rockefeller's and the Rothschild's are part of that organisation. I believe the evidence points to Beyonce being involved in Satanism or other cultish activities such as that. In the book"A Trip into the Supernatural" by a repentant Satanist he says that many of the people in his Satanic temple were aided by supernatural beings to gain their high positions. These included many famous people and singers. Beyonce's occult messages in her music videos and concerts suggest a similar aspect for her. I'm not saying she is a bad person, but she might be caught in the wrong crowd. :|
Anytime a person hears about a secret society, you can usually expect that there's a conspiracy theory in play. Those ideas are mostly bunk backed up only by wild circumstantial evidence. Plus, why would it matter? Beyoncé sings pop songs; she doesn't start wars and send soldiers off to do. She does not have any hold over economic power. Politically speaking, Beyoncé is useless.
Beyonce is not in the Illuminati. People saying this sound absolutely ridiculous. There is no concrete evidence that says she is. The accusations being spat by people are from individuals that want to come up with a lame reason why someone else is successful at what they do and they aren't.
"Does ____ belong to the Illuminati" is a question that the answer to is always no. When it's thrown around with politicians it's simple paranoia in effect, when it delves into musical performers (which it does at a depressingly frequent rate) we're just getting ridiculous here. There is no rational argument to be made for this.
The Illuminati (should they exist) don't gain any significant advantage from being a clandestine operation- meaning they don't need to be secret to accomplish the goals often associated with them. Since Beyonce also doesn't gain any significant benefit from being part of the organization (she became rich and famous through Destiny's Child, and it would be difficult to silence the other two members after splitting Beyonce from them), she doesn't have any reason to secretly belong to such an organization.