In a small ceremony on Thursday in the centre of the northern English city of Liverpool where Lennon was born and raised, fans and officials created a shrine beneath a statue of the legendary Beatle and a priest read out a prayer in his memory.
The city is also holding a memorial service for the man who created some of the world's best-known songs and is considered one of the most influential songwriters of all time.
In New York, scores of people gathered at the Strawberry Fields section of Central Park near the Dakota Building where Lennon lived and where Mark David Chapman murdered him. An evening vigil will be held at 10.50pm (0350 GMT Friday), the time Lennon was shot.
"I first came here the night he was shot. The world misses the music that he and Paul (McCartney) put together," said Andrew Kaplan, 40, at Strawberry Fields.
Friends in Liverpool remembered Lennon with fondness, but felt he distanced himself from them after meeting Yoko Ono, the woman who many fans blame for breaking up the Beatles in 1970.
"You couldn't approach John at the end, and looking back it was from the moment ... he met Yoko Ono," said former friend Billy Kinsley, who knew Beatles Lennon and McCartney in the 1960s.
His assessment of Lennon and the Beatles as musicians, however, has never changed.
A 1969 letter documenting the
Beatles' impending break-up
"It really did make a big impression on me seeing the Beatles on that first night at the Cavern, because it just changed my outlook," he told Reuters in a makeshift recording studio in his garden, recalling the night in February 1962.
"I thought 'My God, I have just seen the best thing that I could ever see', and since then it's been downhill because I've never seen anything as good as the Beatles."
On Thursday visitors from Japan and Spain gathered outside the Cavern Club in Liverpool.
"I usually come every year, but this year is very special," said 26-year-old Estefania Soriano from Spain.
In New York, fans arrayed flowers, incense sticks, and record albums on the Imagine mosaic in the middle of the Strawberry Fields. Most were silent, but some sang Lennon and Beatles songs.
"It's just the sort of thing that happens here. You sing with a new batch of people every year," said David Bertke, a New York financial writer who has come to Strawberry Fields every 8 December since moving to the city in 1990.
Alvaro Maldonado came from Pamplona, Spain, to pay tribute to Lennon. "It's like Jesus Christ. He is a man who brings peace to the world," Maldonado said.
"He was the father I loved who let me down in so many ways ... it's painful to think that his early death robbed me of the chance for us to know each other better"
John Lennon's son
Lennon's legacy was remembered at Thursday's Grammy Award nominations that included a best album nod for Paul McCartney.
"John Lennon influenced everybody in their music whether they know it or not," said singer Mariah Carey after she was nominated for eight Grammys.
Yet the man who brought a generation pleasure with seminal tracks like Strawberry Fields Forever, Give Peace a Chance and Imagine, also caused pain to those who loved him.
Sense of rejection
Both his first wife Cynthia and their son Julian recently voiced their sense of rejection when Lennon left them for Ono.
Cynthia told Reuters earlier this year that she and Julian were "airbrushed" from the Beatles' story and that Ono made it clear she did not want her in New York after Lennon's death.
On his website, Julian added: "I have always had very mixed feelings about Dad. He was the father I loved who let me down in so many ways ... it's painful to think that his early death robbed me of the chance for us to know each other better.
"It's just too painful for her to discuss," he said.