Irvine-based accounting firm WilsonMorgan LLP has merged into the Orange County office of New York-based Marcum LLP.

Marcum has 56 employees in its Irvine office, including 14 partners. Five WilsonMorgan partners and a staff of 30 are expected to join Marcum.

The combined firm will be among the largest accounting firms with headquarters or significant operations in OC. Marcum was No. 31 on the Business Journal’s most recent list of the largest accounting offices here. WilsonMorgan was No. 27.

Steve Rapattoni of Marcum will remain partner in charge of the combined operations here.

Marcum has about 1,200 employees throughout its 20 offices in the U.S. and abroad. It has maintained an Irvine office since its merger with Los Angeles-based Stonefield Josephson Inc. in 2010.