Most of the paintings, including watercolors and oils, were discovered by the Cook County public guardians office, which inventoried and cleaned the house after Margaret Tikalsky moved to a nursing home, the Chicago Tribune reported.
Juergens, born in 1866, returned to his native Chicago after studying art in Europe.
Richard Norton, who owns a gallery specializing in American art, said the Tikalsky collection could revive Juergens' reputation.
"One of the issues has been, there haven't been many important Juergens paintings that surface for sale," Norton said. "If 70 have been in one spot for all these years, that would explain why. This will renew appreciation for the artist."
The paintings were purchased by Tikalsky's father, Francis, a friend of Juergens. Francis Tikalsky, as a teenager, knocked on the painter's door and told him he wanted to learn about art.