Howard A. Tullman — CEO of Chicago tech incubator 1871 in the Merchandise Mart — is stepping down after four years in charge of the organization that’s provided fledgling inventors, designers and web-based businesses low-cost office space and more, according to a memo obtained by the Sun-Times.

“Howard and I have been discussing the next steps for both of us at 1871 for quite some time and have agreed that he has more than fulfilled his commitment to all of us serving an incredible 4 years which has marked unparalleled growth in 1871 and the overall Chicago entrepreneurial eco-system,” wrote James J. O’Connor, board chair of the Chicagoland Entrepreneurial Center, which oversees 1871, in a memo to the organization’s board.

“When Howard took over the reins, we thought he might be able to squeeze in at most 2/3 years and it has been our honor to have him serve so long and so well as our CEO.”

Reached Wednesday, Tullman declined to comment. “When we’re in a position to speak about it, we will,” he said.

He later told Crain’s Chicago Business he’ll be stepping down at the end of the year. “It’s the right time to step out,” he said. “I’m a builder. I enjoy (1871), but there are a lot of other things I enjoy, as well.”

O’Connor, a managing director at the William Blair investment firm, also said in the memo that a consulting company has been retained to find Tullman’s replacement. Additionally, he announced he will begin transitioning out as Chicagoland Entrepreneurial Center chairman, serving in that role another year.

Multiple calls to O’Connor were not returned.

Named for the year that the Great Chicago Fire destroyed most of Chicago and led to its rebirth, 1871 “promotes and grows the startup community in Chicago,” by establishing partnerships “that provide entrepreneurs with the tools they need to build successful, sustainable businesses,” according to its website.

Mayor Rahm Emanuel, who called Tullman a “dear friend, to me and to this city,” has frequently visited 1871’s office space, which has become a part of the city’s efforts to attract tech companies from around the world.

Tullman’s “innovative leadership has helped fuel Chicago’s expanding tech sector and support the growth of hundreds of businesses across the city,” the mayor said in a statement. “Howard has mentored countless entrepreneurs and startups that are creating new jobs and changing the face of Chicago’s digital economy, and he has transformed 1871 into one of the leading technology incubators in the world.”

Besides heading up 1871, Tullman is general managing partner for the Chicago High Tech Investment Partners LLC and for G2T3V LLC – both Chicago-based early-stage venture capital funds, according to his biography on the 1871 website. He has founded more than a dozen high-tech companies.

Contributing: Fran Spielman