The constituency office of SDLP East Derry MLA John Dallat has been attacked.
A large plate-glass window was smashed at the Kilrea premises overnight.
Mr Dallat said hundreds of pounds worth of damage had been caused.
"I am grateful to everyone that offered help," he added.
"These are the real people that I and my party represent and not those who, for whatever reason, decide to attack democrats involved in the political process."
He said over the years he had been extremely lucky to survive in bad times.
"It comes, therefore, as a disappointment that, as we slowly but surely build a stable society, there are still some people who have tendencies towards wanton vandalism and destruction," he added.