More than 1,000 of the theater's 1,300 seats had been reserved by Thursday morning, Giffin said.
"If that's any indication of the festival's growing, we're looking forward to Saturday," she said.
Saturday afternoon's downtown street party is one of the most popular attractions of the three-day festival.
This year's headliner is Clarence "Gatemouth" Brown, a seven-time Grammy nominee and multiple winner of the W.C. Handy Blues Award.
Also featured Saturday will be guitarist Deborah Coleman, who returns to the festival for a second year with her band, "the Thrillseekers," and vocalist Shemikia Copeland, daughter of Texas blues guitar legend Johnny Clyde Copeland.
The concert is free, but admission to the seating around the stage is $7 for adults and $3 for children ages 5 to 12. Shirt and shoes are required and only service animals are allowed.
On Sunday, people are encouraged to take chairs and blankets to City Park for a free concert featuring Clarence Spady, Rory Block, Fil and other artists.
Festival organizers will sell an even bigger variety of merchandise this year. New this year are two new types of T-shirts and a denim shirt sporting the festival's logo.
The festival's official kickoff is this morning at 11:30 in front of the Maryland Theatre with local talent The Rhythm Kings and The Bob Flurie Band.
But the blues already started playing Thursday, with a concert at the Miller House.
About 125 people crowded the rear garden of the historical home on West Washington Street.
The musical stylings of Carl Disque and KoKo Blue provided the background for an evening of music, refreshments and socializing.
The party is a good way to encourage younger people to taken an interest in the Washington County Historical Society and become members, said Lee Stine, who is president of the organization.
People from all over Washington County traveled to Hagerstown for what Stine calls "the unofficial start to the Blues Fest," at the Miller House, an 1830s Federal-style building.
The garden's five-foot brick walls, brick walkway, flowers and ornamental trees provided an intimate setting for the occasion, said Stine. Wine, beer, fruit, cheese and dips were provided for attendees.
For Henry Miller, Thursday's event was a chance to visit the home in which he was born and grew up. His family donated the house to the historical society in the 1960s.
"I'm glad to see the house used like this," Miller said.
"It's a great party. Everyone really enjoys the good food and good music," he said.
Staff Writer Kimberly Yakowski contributed to this story.