FantaSci in Durham, North Carolina, the last weekend in March each year. In 2023 it will be held at the Hilton Doubletree at Raleigh-Durham Airport, from Friday, March 24 to Sunday, March 26.
From their webpage,
FantaSci is a convention by the fans for the fans that is dedicated to raising the awareness of, and appreciation for, science fiction and fantasy in all its forms with a primary focus