Charles L. Ulricson (1816, Stockholm, Sweden – 1887, Peoria, Illinois) was a Swedish-born American architect, who practiced in Peoria, Illinois. He is best known for designing Old Main (1856–57) – the principal building at Knox College, Galesburg, Illinois – now a National Historic Landmark.
The son of Carl Ulricson, architect to the Swedish crown, he graduated from the Royal Institute of Architects in Stockholm. Following his father's death, he emigrated to the United States in 1835, initially settling in New York City. He was employed by the architect Alexander Jackson Davis for about four years, where he worked on University Hall (1833–37, demolished 1890) for New York University. Searching for a place to set up his own practice, he traveled through the American South before settling in Peoria, Illinois, about 1844.
Ulricson established a successful practice in Peoria, designing and often acting as contractor for commercial buildings and residences. He designed and built St. Paul's Episcopal Church (1850, demolished 1880s), of which he was a member and later vestryman; and a private school, Peoria Academy (1854). He designed and built a number of Italianate and Second Empire mansions on Peoria's West Bluff, overlooking the city and the Illinois River.
His most prominent early commission was for buildings at Knox College. The Female Seminary (1856–57), the first education building and dormitory for women, made the college co-educational. Old Main, the centerpiece of the campus, contained men's classrooms and the college chapel. His Victorian Gothic design for Old Main was inspired by Hampton Court Palace, Henry VIII's residence outside London.
Notably, a year after its opening, Old Main was the site of the October 7, 1858 debate between incumbent Senator Stephen A. Douglas and challenger Congressman Abraham Lincoln. A crowd estimated at 15,000 people stood on the lawn for the 3-hour event, while the contenders spoke from a platform erected before the building. The primary subject of the Lincoln–Douglas debates was the expansion of slavery in the United States – Douglas argued in support and Lincoln opposed. Lincoln lost the 1858 Senatorial election, but two years later won the 1860 Presidential election. Old Main is the only surviving building from the debates.