The collection - comprising 88 boxes with Ilyin's papers, books and other belongings - will be studied by Russian archivists before being sent for permanent storage to the library of Moscow State University (MGU).
MGU head Viktor Sadovnichy said it would take about a year to work through the archives, adding that an electronic version would also be made available.
"The return of the archives is a priceless gift," he said, adding that the philosopher's ideas about patriotism were highly important today.
Ilyin's works are frequently quoted by President Vladimir Putin in his speeches.
"Speaking about the key principles on which the Russian state should be based, the renowned Russian philosopher Ivan Ilyin said a soldier was a high and honorary rank representing national popular unity, the Russian state will, strength and honor," Putin said in his May 10 state of the nation address.
Professor Yury Lisitsa, a researcher of Ilyin's legacy, said half of the collection had never been previously published.
Russia paid $60,000 for the collection, including a major contribution from Viktor Vekselberg, a billionaire who is perhaps best known outside the country for returning a Faberge jeweled egg collection to Russia.
Ilyin, a philosopher of religion, was known as an outspoken critic of Bolsheviks and was forced to flee Soviet Russia after the 1917 revolutions. He died in Switzerland in 1954 and his archives were taken to Michigan University in 1965 by his friend and follower Nikolai Poltoratsky for safekeeping.
In 2005, the remains of Ilyin and General Anton Denikin, a leader of the anti-Bolshevik "White" movement, were reburied in Russia.
