Mr Allingham lived in Eastbourne for 40 years
A tree has been planted and a plaque unveiled in memory of the late Henry Allingham, who was one of Britain's last World War I veterans.
Eastbourne Borough Council planted the Austrian pine at the Redoubt Fortress and Military Museum.
Mr Allingham was the world's oldest man when he died last July, aged 113.
The veteran lived in Eastbourne for 40 years before moving to st Dunstans care home in Ovingdean for the last years of his life.
The plaque was unveiled by the Mayor of Eastbourne Carolyn Heaps alongside Dennis Goodwin, who chairs the First World War Veterans' Association.
It reads: 'Henry Allingham, 6th June 1896 - 18th July 2009, A revered gentleman.'
Cllr Steve Wallis said: "Henry Allingham was not only a war hero, but a resident and friend of Eastbourne.
The plaque was unveiled at the Redoubt Fortress in Eastbourne
"He was an inspiration to many and it is fitting we remember this fine gentleman in this way."
Mr Allingham joined the Royal Navy Air Service in September 1915 before transferring to the RAF in April 1918.
He became Britain's oldest ever man in March 2009 when he reached 112 years and 296 days, surpassing Welshman John Evans who died in 1990.
Hundreds lined the streets of Brighton to watch his funeral on 30 July 2009 where guests included the Duchess of Gloucester and senior figures from the Royal Navy and the Air Force.
Mr Allingham was buried with full military honours.