John T. Culbertson, Jr., began practicing law in his home town of Delavan, Illinois, in 1916. John T. Culbertson, Sr., was elected county judge in 1930, and circuit judge in Tazewell County, Illinois, in 1934, serving until 1968. He served on the Illinois Appellate Court for some thirty years, and was appointed to the Illinois Supreme Court in 1969.
In 1926, Robert M. Culbertson, Sr., joined his brother John in the practice of law in Delavan, and continued to practice alone when John was elected to office. In 1956, Robert M. Culbertson, Jr., joined his father in the practice which became Culbertson & Culbertson. In 1977, Mark E. Allen joined the firm, which became Culbertson, Culbertson & Allen in 1980. Robert M. Culbertson, Sr., passed away in 1985, and Robert M. Culbertson, Jr., retired in 2009, leaving Mark E. Allen as the sole practicing attorney with the firm, which became Culbertson & Allen, LLC, in 2009.