Around 1,200 mourners attended the service or stood for the vigil in the first hour, according to Litchfield cathedral's authorities.
Among those attending and giving their thumbs-up were Celia Houghton and her 14-year-old daughter Freya, who had attended school with Stephen.
The teenager remembered a powerful speech the young man gave to the school's assembly a year ago, saying "he was one person who stood out".
Freya added: "The one thing that spoke to me was when he said 'don't measure time by the clock, measure it by what you do'.
"When he died, people cried at school.
"I remember walking along the corridor and people were using Post-It notes to stick goodbye messages on the wall."
Her mother said they had run to catch the horse-drawn hearse as it had left Stephen's home earlier, wanting to be there to mark the moment.
More than 10,000 people joined Stephen Sutton's family and friends in paying an emotional farewell to the inspirational teen cancer victim.
We were inundated with responses after asking our Facebook readers to post 'thumbs up' pictures in tribute to Stephen Sutton.
Mourners turned out to celebrate the life of teenage cancer victim Stephen Sutton as the fund he launched topped £4 million.