Two prominent, family-run Princeton real estate firms have merged to form one new company. Announced on January 10, Henderson Sotheby’s International Realty and N.T. Callaway Real Estate, LLC, are now known as Callaway Henderson Sotheby’s International Realty. The sign outside the former Callaway office on Nassau Street was changed immediately to reflect the new identity, as was the website for the two firms.

“It was the best kept secret Princeton ever had,” said Pete Callaway, who founded the Callaway company and is now the managing broker for the new entity. “Everyone on our team and the Henderson team were all sworn to secrecy, and I am absolutely amazed that it didn’t get out until Tuesday [January 10]. The word had not hit the street. And no one knew here.”

According to Mr. Callaway, the office at 4 Nassau Street will serve as headquarters for residential real estate. “All of the agents at Callaway and Henderson in residential sales will work out of this office,” he said. “I think at Henderson’s Chambers Street location, we are going to move our commercial department, real estate management, and marketing. We feel that’s probably the best thing.”

The Henderson family owns the building at 34 Chambers Street, while the Callaways have a minor ownership in 4 Nassau Street. Under the merger, the newly combined firm will operate five offices located in Princeton, Pennington, Cranbury, Montgomery, and Lambertville. Sotheby’s International Realty Affiliates is a network of nearly 12,000 sales associates located in approximately 590 offices in 44 countries.

The Callaway and Henderson firms have long histories in Princeton. Mr. Callaway founded N.T. Callaway Real Estate in 1974. In 1976, he was the initial broker for Sotheby’s when that company opened Sotheby’s International Realty in Princeton. “From there, they grew to about 180 agencies in the country, and then they sold to Cendant,” he said. “We were then told we would have to become a franchisee and lose our logos. I had worked very hard to build our company and our logos, and I didn’t want to do that.”

So Mr. Callaway went off on his own, and Sotheby’s eventually allied with Henderson. About seven months ago, Mr. Callaway said, Sotheby’s asked him if he would be interested in coming back to the company. “But that would necessitate joining forces with the Henderson organization, and they had the exclusivity to the Sotheby’s site,” he said. “That got us talking to the Hendersons about it. We felt that in this difficult market, joining the two firms would be a great thing.”

The Henderson firm dates back to 1953, when John T. Henderson Sr. opened an office at 116 Alexander Street. “My grandfather started the company, and then my parents ran it from 1968 to 1998, when they sold it to Gloria Nilson,” said Judd Henderson, who is now managing member of the new firm and co-manager of the Princeton office. “I reopened it as the Princeton Real Estate Group in 2001. Then in 2005, we became a Sotheby’s affiliate. And now, we’re combined with Callaway.”

Along with Mr. Henderson, and Mr. Callaway, the new firm will be led by Matt Henderson, Jane Henderson Kenyon, Norman Callaway, and Karen Callaway Urisko.

“I’m the older generation, if you will,” said Mr. Callaway. “I’m going to be the managing broker. I think this will give Norman and Judd time to work together to run a very large organization, and that’s a healthy thing. We’ll all work together to get it off the ground. We’ll all be able to help each other in this difficult market, though we do feel that the bottom has been found as far as real estate prices go.”

The Callaway and Henderson firms have represented some of the costliest real estate in the area. Current offerings on the newly combined website include the historic Tusculum estate, with more than 23 acres and a 2,000-bottle wine cellar, for $8.975 million; and a $4.7 million brick mansion on Hodge Road.

Longtime rivals for the big-ticket listings, the two families will now be co-existing in one firm. “We were competitors,” says Mr. Callaway. “But we’ve known the Hendersons for years.” Mr. Henderson added, “I’ve always gotten along personally very well with them. That’s what enabled this to happen. The fact is it was an extremely amicable process and it went very well. The whole thing exceeded my expectations. It’s been great.”

What makes the merger unique is the fact that it is still, despite the affiliation with mega-company Sotheby’s, a family business. “The most important thing to our agents and our clients is that we want to give people a local, family-owned option,” Mr. Henderson said. “We still wanted that to be the case. This enabled that to continue, hopefully for another 60-plus years.”