The site upon which Ellsworth School now sits originally was occupied by an annex for the Lisle Graded School, which was declared inadequate in 1876 for the pupils living east of Washington Street.
The second Lisle Graded School was built for "the advanced class" after voters agreed by a vote of 26-4 that directors Edmund Stover, S. Riddler and M.S. Ellsworth could purchase the current Sleight Street site.
In 1884, a two-story brick addition made it possible to house all grade levels in the Sleight Street building. In 1898 a group of concerned citizens convinced the community to support the cost of replacing both structures at a cost of approximately $106,350.
It was named Ellsworth School in 1891, in honor of Lewis Ellsworth, who had been in 1863 the first "School Commissioner of DuPage County," and for Milton Ellsworth, who had served from 1868-1877 as the ""Director and Clerk of District 7."
In 1911, District 7 and District 78 on the west side of Washington merged as School District 78 under a seven-member Board of Education. All 116 high school students attended a four-year program of classes in the remodeled upper floors at Ellsworth. First through fifth graders from the east side attended Ellsworth School, but all seventh and eighth graders attended Naper School on the west side of town. In 1916, the high school students moved out of Ellsworth to their very own building located at the corner of Washington and Spring Street (current Washington Jr. High School site).
Ellsworth's English architecture and high ceilinged rooms encompass terrazzo floors and lime stained oak woodwork and cabinetry—even window seats and a fireplace (non-functional) in the kindergarten room. Both Ellsworth and Naper Schools were designed by architects from Warren S. Holmes Co., who believed that an attractive physical environment enhanced the learning process. Each was built to accommodate the newly instituted grade of "kindergarten" and one class of each grade one through six. Considered advanced for their day, both Ellsworth and Naper School's were equipped with gymnasiums, libraries and an art and music room.
During the 1950's Ellsworth School gained a four-room addition, and in 1974 a temporary wing was added to house the school's Learning Resource Center (LRC). In 1982 the temporary structure was removed and a wing containing an LRC, a computer lab and administrative offices was added at a cost of approximately $226,000.