Your best bet would probably be big crowds, though not so large as they would be if the 4th was on a Friday-Saturday-Sunday. A lot of locals will be there certainly with the day off work for many businesses, and generally the crowds do not die off as much in the evening because many people will stay for the park's fireworks.
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html