Leslie Copus Peltier was born in Delphos, Ohio. Delphos is located in northwestern Ohio in both Van Wert and Allen County. His homeplace was located on South Bredeick Street, and his home is still standing today. The home was known as Brookehaven. Peltier married Dorothy Nihiser in November 1933. An amateur astronomer, he was a prolific discoverer of comets and also a persistent observer of variable stars and member of the AAVSO. Harlow Shapley once described him as "the world's greatest non-professional astronomer".
He wrote the heart-warming autobiographical Starlight Nights (ISBN 0-933346-94-8), which evokes the magic of stargazing in simpler days, on a farm and without light pollution.