The 31-year-old, who played singing quarterback Finn Hudson in the hit show, died from an alcohol and drug overdose in a Vancouver, Canada hotel room on 13 July, 2013, and three years on, friends and fans of the hit TV musical series took a moment to mourn his passing on Wednesday (13Jul16).
The hashtag "#3YearsWithoutCory" began trending on Twitter as devotees marked the death anniversary, and a number of his former castmates also took to social media to share their continued grief.
Morrison was among the first of Cory's Glee family to comment on the poignant date, as he posted a screen grab of the pair in character.
"The minutes become days, and the days become years... but you always remain so close," he wrote. "I miss you, Brother."
Kevin also uploaded a funny gif of the two pals messing around, and captioned it: "Today I woke up thinking abt ur (about your) smile & how infectious it was. U made us laugh & feel loved evryday (sic). #3YearsWithoutCory".
Glee star Lea Michele, who was Cory's girlfriend both on and off screen, shared a picture she had taken of the actor on a beach, and commented, "I know everyday you're watching over me, and smiling. Love and miss you Cory, everyday, but today a little more..."
The actress, who split from her latest boyfriend, Robert Buckley, earlier this month (Jul16), recently had a permanent reminder of Cory tattooed on her torso - the number '5', a nod to his character's jersey number.
Meanwhile, Naya Rivera wrote: "Always missed and never forgotten", and Jenna Ushkowitz added: "The time may pass but the warmth of your generous soul and the humility in your goofball nature will never fade. You are and always will be our quarterback. we miss you, friend".
And actress Heather Morris revealed she had tried to keep her emotions in check as she mourned the loss of her friend, because she was pregnant with her first child at the time of his passing.
"Three years ago my best friend was about to get married, I was 7 months pregnant and was delivered the news that Cory had passed," she recalled. "I was weary to get too emotional in fear that I would go into labor too early."
Alongside a picture of Cory sneaking a photo of Heather as she attempted to shave the hair on her chin on set, she continued, "Not only was cory the most genuine, always the guy to stop and say hi to fans, but he made everyone around him laugh....obv (obviously) this photo is proof. He was our family. We miss u bud. #3yearswithoutcory".