A war memorial stone was smashed and poppy wreaths shredded during an overnight attack.
Police said it was investigating the vandalism outside Killowen Orange Hall in Coleraine on Saturday morning.
The memorial was formally dedicated two years ago in memory of those killed in both the First and Second World Wars.
George Duddy, district master of the Orange Order in Coleraine, said he was disgusted at the actions of the perpetrators.
"This heinous act is not only an insult to the entire community of Coleraine but also to those who sacrificed so much on the front line so that we enjoy the freedoms we have today," he said.
"While those we remember served their country in uniform with honour, the culprits of this reprehensible deed offer nothing but shame.
"They must not be allowed to succeed and local brethren are determined their mark of respect to the war dead is re-instated to its rightful place."
Damage to the memorial garden, stone and wreaths were discovered at 7am.
Police are investigating if the incident was an act of vandalism or a targeted attack.
The PSNI has appealed for anyone with information to come forward.