Write Express contains sample text for a thank you letter. These examples are designed specifically to thank people for attending an event. The letter should begin by expressing appreciation to the recipient.
Phrases such as "it was our sincere pleasure to have you at our event" or "thank you so much for attending (name of event)" are appropriate. It may be fitting to thank people associated with the recipient as well, such as a business person's secretary or professional team. It is acceptable to include a short recap of the event. If the recipient made a donation or provided valuable input at the event, this should also be mentioned in the letter, along with additional thanks.