The foundation has seven members, four are elected by the residents of the old Masterton County Council, two are appointed by the Masterton District Council and one appointed by the Guardian Trust as trustees of the original Trimble estate.
The foundation came into being in June 2004 in accordance with the Masterton District Council (Montfort Trimble Foundation) Act 2003.
After the 2004 local body elections two of the elected members will retire at each local body election and are able to be re-elected.
After the 2016 elections the Foundation members are:
- Andy Pottinger (chairman; appointed by the Guardian Trust)
- Roddy McKenzie (elected for two terms in 2016)
- Harriet Palmer (appointed by the Masterton District council)
- Robin Dunlop (appointed by the Masterton District council)
- Stan Braaksma (elected for two terms in 2013)
- Mike Wyeth (elected for two terms in 2010)