National's new office in Kerikeri is the only one in the country without a local electorate or list MP, the party says.
Rodney MP Mark Mitchell, who formally opened the out-of-Parliament office last week, said it signalled National's "total commitment" to Northland.
"People may have expected us to close shop, but that was never going to happen," he said.
National lost the electorate in March to NZ First leader Winston Peters in a byelection forced by the resignation of MP Mike Sabin for "personal reasons".
It was the first time since 1966 any party but National has held the seat. Orewa-based Mr Mitchell aims to hold monthly clinics in Kerikeri.