The report contains several examples, including times Comey sent himself drafts of a testimony he planned to deliver to Congress and drafts of bureau-wide updates he planned to send to mark milestones during the year.
Using personal email for work purposes is "inconsistent" with DOJ policy, given a lack of "exigent circumstances and the frequency" at which the use occurred, the report says.
Clinton responded Thursday to a description of Comey's actions with a tweet:
The FBI investigation in 2015 and 2016 looked into whether Clinton and others deliberately sought to handle classified information improperly on her personal email account and server while she was secretary of state.
Comey in July 2016 announced that, while he found Clinton's actions "extremely careless," he would not recommend charges against her. That October, he informed Congress that FBI agents had recovered additional emails possibly relevant to the Clinton probe.
Asked by IG investigators if he had any concerns about conducting bureau business on his personal device and account, "Comey stated that he did not," the report says.
He also said he was certain his work would be captured by FBI email servers for record-keeping purposes.
"Because it was incidental and I was always making sure that the work got forwarded to the government account to either my own account or [FBI chief of staff James Rybicki], so I wasn't worried from a record-keeping perspective and it was, because there will always be a copy of it in the FBI system and I wasn't doing classified work there, so I wasn't concerned about that," Comey told investigators, according to the report.
Comey added that he did not use his personal email or laptop for classified or sensitive information, and only did use his personal email "when I needed to word process an unclassified (document) that was going to be disseminated broadly, (such as a) public speech or public email to the whole organization," the report says.
Clinton has also said she did not use personal emails for classified purposes and stressed that her messages were captured by State Department servers at some point.
Other examples cited in the IG report include emails Comey forwarded from his unclassified FBI account to his personal account containing corrections to a newspaper article he had sent to bureau officials, and proposed responses to requests for information from a federal agency.