Keeler was born in La Salle Illinois, but grew up and spent the majority of his early life in Mayport, Florida near Jacksonville.

After this feature had been named for Johann Encke, who had observed a much broader variation in the brightness of the A Ring,[3] Keeler's contributions were brought to light.

[9] This was the first observational confirmation of the theory of James Clerk Maxwell that the rings are made up of countless small objects, each orbiting Saturn at its own rate.

In 1880, Allegheny Observatory director Samuel Pierpont Langley, accompanied by Keeler and others, went on a scientific expedition to the summit of Mount Whitney.

The purpose of the expedition was to study how the Sun's radiation was selectively absorbed by the Earth's atmosphere, comparing the results at high altitude with those found at lower levels.