The average person is expected to spend $83 in the county that weekend, according to state estimates.
"That is extremely conservative, but I feel much more comfortable with a conservative figure than I do with an exaggerated one," he said.
There are 1,700 rooms in county hotels, motels, bed and breakfast inns, and all are booked for the nights of Sept. 12 and 13, Larsen said. Requests for the Thursday night before the event and the Sunday night after are also filling up, he said.
Winnie Price said there's no room at her Wingrove Manor bed and breakfast in Hagerstown for that weekend, nor does she have any vacancies at the Carriage House inn she owns in Waynesboro, Pa. She estimates she has had to turn 20 people away.
"We've been booked for months," she said.
Other businesses also expect to reap the benefit of an estimated daily crowd of 60,000 spectators and re-enactors expected to fill the Rench Road farm where the event will be held. Area stores, gas stations and restaurants are all expected to see added business because the re-enactment, he said.
"It's going to be a huge demand on our service sector that weekend," Larsen said.
Charles Sekula, owner of the Schmankerl Stube Bavarian Restaraunt in downtown Hagerstown, estimated his business will increase by about a third that weekend. He anticipates many vistors coming to the re-enactment will make their dinner plans after they get here, rather than make reservations ahead of time.
"I think everybody should prepare for that," he said.
Valley Mall in Halfway is planning several marketing efforts during the weekend, from hosting a living history show with Civil War re-enactors on Sept. 14 to sending "goodie bags" filled with coupons and other promotional materials to guests at area hotels.
"We knew this was going to be a huge draw to the county, and certainly we didn't want to miss the boat," said Stephanne Saunders, marketing manger for the mall.
There are no estimates on how much impact the re-enactment will have on the mall's business, but Saunders said she expects there will be many more people on hand than on a normal weekend. In preparation, the mall sent notices to its stores, asking that extra staff be put on call.
Unlike the re-enactment coordinators, who worry that inclement weather could hurt attendance to their event, Saunders said a downpour could have just the opposite effect on the mall
"If it rains, we are going to be swamped," she said.
An obvious beneficiary of the re-enactment is expected to be Antietam National Battlefield, where between 35,000 and 40,000 visitors are expected each day, said Superintendent John Howard.
Howard said the entrance fees paid by visitors - $2 per person and $4 per family - will help with the maintenance of the National Park System. The battlefield's bookstore, which is run by the nonprofit Parks and History Association, is expected to bring in $4,000 to $6,000 a day, he said.
The economic impact of the re-enactment is also spilling across the county line, too. Larsen said because there is no available lodging in the county for the weekend, people have been forced to look to Frederick County, as well as Pennsylvania and West Virginia, for places to stay.
Two Frederick hotels are already booked for the night of Sept. 13, and about five to 10 calls a day are made to the Tourism Council of Frederick County's office from people interested in the re-enactment, said Beth Rhoades, the agency's tour marketing coordinator.
"It seems like it's steadily increasing," she said.
Tourism officials and business owners hope the re-enactment weekend will not only bring a one-time boost to the local economy, but also be the centerpiece of the ongoing effort to make the Hagerstown area a Civil War destination - something they believe could benefit the area for years to come.
"This is just a kickoff, and I think it will have an enormous impact on everyone," Sekula said.