The Health Secretary, Jeremy Hunt, has apologised on behalf of the NHS for failing to spot the signs of sepsis which killed a little boy from Penryn.
He attended Truro Cathedral on Saturday, to show his support for William's mother, Melissa Mead, who has helped raised the profile of the deadly disease.
In December, they launched a nationwide campaign, which has introduced a series of measures in hospitals to tackle the condition.
At the service in Truro, which celebrated the life of William, Jeremy Hunt spoke about the one year-old who "should have been enjoying beautiful Cornish sunshine with his parents."
William Mead died from Sepsis in December 2014, after doctors repeatedly failed to spot his symptoms.
A report into his death criticised GPs, out-of-hours services and a 111 call handler who failed to spot the symptoms.
In January 2016, Health Secretary Jeremy Hunt apologised in the House of Commons on behalf of the NHS for William's death.
His mum, Melissa, has campaigned tirelessly to raise awareness of the disease, helping create a check-list of danger signs with Public Health England.
Sepsis, also known as septicaemia or blood poisoning, is a life-threatening condition that occurs when the body's immune system goes into overdrive as it tries to fight an infection.
At the service, Melissa spoke of wanting to remember the "boy that lived".
She said, "he gave his life so unnecessarily but he's saved so many others. It's wonderful and beautiful to be able to come and celebrate his life."
"It's vital to keep the spotlight going on sepsis and we want to continue working with the government to make everyone more aware of the condition."