In 1900 Willa Cather was a newspaper reporter living in Phildelphia. The author of O Pioneers, My Antonia, and other novels of the western frontier had yet to pen her well-known works.
Philadelphia was probably a big change from rural Nebraska where Cather grew up. Her migration trail was little bit atypical. She was born in Virginia, lived in Nebraska and moved to Pennsylvania where she is shown here in 1900.
The 1900 Census can be searched at Ancestry.com--but keep your ancestor's migration path in mind.