GTCR, one of Chicago’s biggest private equity firms, today announced the closing of its tenth buyout fund, with more than $3.25 billion of investor commitments.

The fund had an initial target of $3 billion.

“Fund X is the largest in our firm’s 30-year history, and one of our quickest to raise,” GTCR Principal Phil Canfield said in a statement.

GTCR raised $2.8 billion for its ninth fund in 2006.

Since 1980, GTCR has invested more than $8.5 billion in more than 200 companies.

Fund X will target investments in companies in financial services and technology, health care and information services and technology.

“More than 80 percent of commitments to Fund X came from existing investors,” GTCR Principal David Donnini said. “Of the 10 largest investors in Fund X, more than half have been investing with GTCR since the 1980s.” About half of the fund’s new commitments came from international limited partners, he added.

Investors in Fund X include public pension funds, endowments, foundations, fund of funds and individuals, including GTCR principals as well as select executives and other “friends” of GTCR.

The Teachers’ Retirement System of Illinois disclosed last November that it has committed to invest up to $100 million in GTCR Fund X.