A state audit found that Gov. Bruce Rauner's budget office failed to collect more than $2 million in federal rebates.
The review released Tuesday found that the Governor's Office of Management and Budget never received $2.4 million in rebates owed for payments the state makes on bond debt.
Auditor General Frank Mautino found no evidence the office tried to collect the money. Five other receipts show Illinois left an additional $183,000 combined on the table.
The office is responsible for preparing the governor's annual state budget and tracking revenue and spending.
Mautino also found the office overstated its investment income by $40,000 and did not submit accurate financial disclosures to the state Comptroller.
The budget office agreed with the findings and says it improved its procedures.