After finally traveling to Europe and the Asia Minor in February 1883, Johnston returned to the United States and established his own practice in Minnesota in 1886.
He quickly gained a reputation as a respected domestic architect, designing countless homes and churches in Saint Paul, especially in the vicinity of Summit Avenue and Saint Paul's Hill District.
In 1886 Johnston formed a partnership with William H. Willcox which lasted through 1890.
In 1895 Johnston entered the competition to design the new Minnesota State Capitol, but lost to Cass Gilbert.

On May 22, 1901, the Minnesota State Board of Control, a body responsible for the construction and operation of all state-funded institutions, appointed Johnston as State Architect.
As State Architect, Johnston prepared plans for the Minnesota State Prison, buildings at various state college campuses, hospitals, sanitoriums, and other public structures.
Since state business was at the whims of the Minnesota Legislature and was not always consistent, he continued his private practice during this time.
Retaining private commissions allowed him to operate his office continuously and receive a higher rate of return.
Johnston continued as State Architect until 1931, when the State Division of Construction was dissolved.

Johnston was also architect for the Board of Regents of the University of Minnesota and drew plans for all the new buildings constructed on campus during his tenure.

Johnston never officially retired, but backed off on his practice after the State Architect position dissolved in 1931.
He died December 29, 1936.
After finally traveling to Europe and the Asia Minor in February 1883, Johnston returned to the United States and established his own practice in Minnesota in 1886. He quickly gained a reputation as a respected domestic architect, designing countless homes and churches in Saint Paul, especially in the vicinity of Summit Avenue and Saint Paul's Hill District. In 1886 Johnston formed a partnership with William H. Willcox which lasted through 1890. In 1895 Johnston entered the competition to design the new Minnesota State Capitol, but lost to Cass Gilbert.
On May 22, 1901, the Minnesota State Board of Control, a body responsible for the construction and operation of all state-funded institutions, appointed Johnston as State Architect. As State Architect, Johnston prepared plans for the Minnesota State Prison, buildings at various state college campuses, hospitals, sanitoriums, and other public structures. Since state business was at the whims of the Minnesota Legislature and was not always consistent, he continued his private practice during this time. Retaining private commissions allowed him to operate his office continuously and receive a higher rate of return. Johnston continued as State Architect until 1931, when the State Division of Construction was dissolved.
Johnston was also architect for the Board of Regents of the University of Minnesota and drew plans for all the new buildings constructed on campus during his tenure.
Johnston never officially retired, but backed off on his practice after the State Architect position dissolved in 1931. He died December 29, 1936.
Clarence H. Johnston Sr.