CHICAGO—Aon Corp.'s revenue jumped to $11.29 billion in 2011, a 32.7% increase over that of a year earlier, due in large part to its purchase of Hewitt Associates Inc., the Chicago-based brokerage reported Friday.

Revenue for its Aon Risk Solutions brokerage and risk management unit increased 6.2% over that of 2010 to $6.82 billion, while revenue for its human resources solution unit increased 113% to $4.5 billion. Retail brokerage income in 2011 from fees, commissions and other sources rose 7.7% from that of a year earlier to $5.30 billion.

Aon said the overall rise stemmed from a 29% increase in commissions and fees resulting from acquisitions, primarily of Hewitt, net of dispositions; a 2% increase in organic revenue driven by Aon Risk Solutions; and a 2% favorable impact from foreign currency exchange rates.

Aon’s net income increased 38.7% to $979 million for the year.

For the fourth quarter, Aon’s total revenue increased 3% to $3.0 billion. Aon Risk Solutions’ total revenue increased 6.2% to $6.82 billion and HR Solutions’ total revenue increased 113% to $4.5 billion as a result of the merger with Hewitt, Aon said in a statement. For the fourth quarter, retail brokerage income rose 3.5% to $1.47 billion.

Net income for the fourth quarter increased 19.4% to $277 million.

“Our fourth-quarter results reflect 15% growth in earnings as highlighted by organic growth across all major businesses and the continued delivery of synergy savings related to Aon Hewitt,” Aon President and CEO Greg Case said in a statement. “While macroeconomic conditions remain challenging globally, we are firmly on track to deliver improved growth in 2012, our restructuring programs will deliver cost savings, and we have solid financial flexibility that will drive increased shareholder value, as highlighted by the repurchase of $828 million of common stock in 2011.”

Aon recently announced that it would move its headquarters from Chicago to London in a strategic plan to grow Aon as a global platform.