He then returned to New York to attend Cherry Valley Seminary. Before graduating, he moved to Glenville, New York to operate a mill. Ellwood became interested in the cultivation of broom corn and ran a successful broom business, employing 130 men. He married Eleanor Vedder in 1849; they had six children. He was a member of the New York State Assembly (Schenectady Co.) in 1851 as a Whig. Ellwood was named a delegate to the 1856 Republican National Convention, the party that he would identify with for the rest of his life. He returned to Sycamore in 1857, engaging in the hardware trade, particularly farm machinery. He invested in local farm implement manufacturers and became one of the wealthiest men in the county. Ellwood continued his political aspirations as U.S. Assessor for the 4th Congressional District of Illinois the first mayor of Sycamore.