Sheriff Ronnie Strength said the informant's attorney contacted the department on Feb. 1. The informant, whose name is being withheld by authorities, claimed to have had a relationship with Investigator Daniel Stenger, which began in December.
Strength said the woman had been providing information to investigators in connection to a meth bust in August. The informant's boyfriend was arrested in that bust.
Stenger was not the lead investigator on the case but he had been contributing to the investigation since October.
Strength said he did not think the allegations would derail the drug case against the woman's boyfriend.
"We'll be looking at it with the district attorney but we don't think that it will have any bearing in proceeding with his prosecution," Strength said.
Stenger has been with the sheriff's department for 13 years.