The Lincolnshire Wildlife Trust has celebrated reaching a record 25,000 members.
Founded in 1948, its membership has increased from 10,000 in 1998 to the current figure.
The conservation charity looks after and protects more than 3,500 hectares of land on almost 100 nature reserves.
Lincolnshire Wildlife Trust chairman Sir John Mason said it was a "fantastic achievement, especially considering the current financial situation".
"We are extremely grateful to all our members. It's only through their support that we are able to undertake the work we do," said Sir John.
"It illustrates that people value wildlife and are willing to take part in helping to protect it."
Rachel Shaw from the trust said it was important to have a large and growing membership.
"It helps to make the people who make decisions listen to us a little bit more," she said.