Investigators say the abuse may have begun sometime in the fall of 2007 with a final occurrence taking place last weekend.
Detectives believe more abuse may have taken place and will continue to investigate.
The child is currently believed to be the only victim.
"In all my years of law enforcement, I am still shocked and disgusted anytime I hear of a child being hurt or abused," said Lake County Sheriff Mark Curran. "I am certain our investigators will see this case all the way through in assuring these two get the penalties they so clearly deserve."
The Horak couple have been charged with one count each of predatory criminal sexual assault of a child, a Class X felony. They appeared in bond court Saturday, where bond was set at $500,000 for each of them.
If convicted, the Horaks could face up to 60 years in jail. They remain in the Lake County jail.