If you would like to thank someone for their community service, here is a sample template you can use to write a letter acknowledging community service.
On the behalf of the [Name of Organization], I would like to express my sincere gratitude for your commendable community service. We thank you for the time and efforts that you invested in the cause and to help the community grow.
Your contribution and generosity are greatly admired, and we hope that it offered you a pleasant sense of inner-satisfaction too. We appreciate all your support and generosity that you have displayed in the past few [months/years].
Your work inspires other members too and we are grateful to have you among us.
Thank you and keep up the good work!