"We're preparing for the high end, and not the low end," said Sheriff Darren White.
The sheriff's department is working with other law enforcement agencies to make sure the protest is peaceful.
"Understanding that that's a lot of people to thrust in the downtown area all at once, we want to make sure that they're able to come here and do whatever it is that they want to do, and be safe while they're doing it," said Sheriff White.
The rally grew out of support for the alleged victim Daisy Coleman after the online group - Anonymous - pushed the case into the national spotlight last week.
The rally is set to start at 6 p.m., but roads around the courthouse will be closed as early as 1 p.m.
"We are going to prepare, be prepared, to be able to shut down the streets on pretty short notice if we have to," said Sheriff White.
Police are also keeping an eye out for businesses near the courthouse. Some decided to remain closed until the protest is over.
"We did talk about keeping our door closed. We'll be here in case something gets out of control. Things started flying, and because of people being upset, we just wanna be here in case," said Joe Alonso.
Police will have all hands on deck at the rally, but to make sure things go smoothly, Sheriff White wants everyone to remember one thing.
"If you are going to come here, you know, let's all be peaceful, let's all get along. We don't need anyone doing anything silly that causes anyone to get hurt," said Sheriff White.