He attended public schools in New York before moving to DeKalb County, Illinois with his family when he was fifteen.

After working in a Rockford brickyard, Ellwood had saved enough money to purchase a 160-acre (65 ha) farm near Sycamore, which he tended for four years.

Ellwood was named a delegate to the 1856 Republican National Convention, the party that he would identify with for the rest of his life.

Ellwood continued his political aspirations as U.S. Assessor for the 4th Congressional District of Illinois the first mayor of Sycamore.

He was re-elected to the 49th United States Congress, but before its assembling, he died after a long illness in Sycamore on July 1, 1885.