Howard said the free performance is held each year to thank local people for their support of the park and the orchestra, and as a tip of the hat to independence.
It's a tradition held each year on the Saturday nearest July 4. Each year, people spread out blankets, have picnics and enjoy the day at the battlefield.
People can start arriving Saturday morning, and Howard suggested they get to the park by 5 p.m. because of the anticipated crowd.
"They can come at sunrise if they like," Howard said.
The main routes into the park are Md. 65 and Md. 34.
People can put down blankets to reserve spaces for the show, although they can do that no earlier than 6 a.m. Saturday, Howard said.
About 90 portable toilets have been brought in for the show, and an estimated 60 park workers and about 15 park rangers from other national parks in the region will be at the event, Howard said.
About 60 to 80 volunteers will help pass out pamphlets, pick up trash and help with other duties, Howard said.
No grilling is allowed during the event, although people are welcome to bring chilled food, and coolers are allowed, Howard said.
People who want to pick up food and drinks at the park can do so at a booth the Sharpsburg Volunteer Fire Co. will set up near the visitors center, Howard said.
Although playing Frisbee is generally discouraged at the park, people can do so at Saturday's event while they are waiting for the orchestra to begin playing, Howard said.
Workers begin arriving at the park at about 8 a.m. Saturday and are there until about 1:30 a.m. Sunday picking up trash, Howard said.
Antietam was the site of the bloodiest single-day battle of the Civil War. A total of 23,000 Union and Confederate soldiers were reported killed, wounded or missing in the Sept. 17, 1862, battle.