Segalovich, the company's chief technical officer and a Yandex director from 2000 until his death, was praised for his wealth of technological knowledge, his philanthropy, his business acumen and his high ethical standards.
His death from cancer was unexpected, as he appeared to be doing well recently and posted several notices online that he planned to take part in a political demonstration in Moscow, RIA Novosti reported Thursday.
He could not attend the demonstration because he was out of the country.
"I was friends with Ilya since school; we sat behind the same desk for four years. And then we created Yandex together. Last night he died. Everything happened too quickly and unexpectedly," wrote Yandex co-founder Arkady Volozh in an online posting.
The company was started in the 1990s and debuted as a public company with one of the largest-ever Russian initial public offerings on a foreign exchange, an event that raised $1.4 billion on the New York Stock Exchange in 2011.
Segalovich owned 2.5 percent of Yandex's capital, and 6.87 percent of its shareholder voting rights. The company is now worth about $10 billion, the news agency said.
Russian Prime Minister Dmitry Medvedev said the loss would be felt through "the whole of the Internet industry.
"[Segalovich] was a professional of the highest class, with a kind heart and the ability to inspire and care about those who surrounded him. It is a big loss," Medvedev wrote in a note posted on social networking Web site Vkontake.
Segalovich was born in 1964 in Gorky, which is now Nizhny Novgorod. He attended school in Kazakhstan, before studying geophysics at the Moscow Geological Exploration Institute.
Segalovich donated generously to Maria's Children, an art therapy program for Russian orphans. His wife, Maria Yeliseeva, is a co-founder of the program and its director, RIA Novosti reported.