Johnston started attending Saint Paul High School in 1872 and took on a job as a clerk at the law firm of Rogers and Rogers.
 His mother died May 8, 1874, at the age of 42.
That same year, Johnston quit his clerical job and began work at the firm of Abraham M. Radcliffe as a draughtsman.
Radcliffe's firm was a local training ground for aspiring architects at the time.
 In September 1876, Cass Gilbert joined Radcliffe's firm as an apprentice, and Gilbert and Johnston soon became close friends.

In the fall of 1878, Gilbert and Johnston enrolled at the Massachusetts Institute of Technology (MIT).
There they met James Knox Taylor, who had also grown up in Saint Paul and joined MIT as an architectural student a year earlier.
Gilbert and Johnston, along with Taylor, had opted to take the special two-year course in architecture, rather than the full four-year degree-granting program.
However, Johnston was forced to drop out after one term due to financial reasons.
He moved back to Saint Paul and worked briefly at the firm of Edward Bassford, where the firm was more conscious of costs to the client in the design and construction process.
This influenced Johnston to view economic constraints as a challenge to be solved by inventiveness, instead of being a restriction on his artistry.
During these years, Gilbert and Johnston kept in touch through a large number of letters.

In January 1880, Cass Gilbert departed to Europe for an architectural tour.
Gilbert wrote back to Johnston urging him to make a similar trip, but Johnston was preoccupied with a job offer from Herter Brothers in New York.
One of the projects on which he worked during his tenure at Herter Brothers was J.P. Morgan's brownstone house on Madison Avenue at 36th Street.
In the summer of 1880, Cass Gilbert returned from Europe and settled in New York, working for the firm of McKim, Mead & White.
Gilbert and Johnston, along with their MIT classmate Francis Bacon, shared rooms at 40 Irving Place.
That same year Johnston, Gilbert, Bacon, Taylor, and William A. Bates founded the Sketch Club, which later became the Architectural League of New York.
Accounts vary on which members were actually the founders of the club.
Johnston started attending Saint Paul High School in 1872 and took on a job as a clerk at the law firm of Rogers and Rogers.  His mother died May 8, 1874, at the age of 42. That same year, Johnston quit his clerical job and began work at the firm of Abraham M. Radcliffe as a draughtsman. Radcliffe's firm was a local training ground for aspiring architects at the time.  In September 1876, Cass Gilbert joined Radcliffe's firm as an apprentice, and Gilbert and Johnston soon became close friends.
In the fall of 1878, Gilbert and Johnston enrolled at the Massachusetts Institute of Technology (MIT). There they met James Knox Taylor, who had also grown up in Saint Paul and joined MIT as an architectural student a year earlier. Gilbert and Johnston, along with Taylor, had opted to take the special two-year course in architecture, rather than the full four-year degree-granting program. However, Johnston was forced to drop out after one term due to financial reasons. He moved back to Saint Paul and worked briefly at the firm of Edward Bassford, where the firm was more conscious of costs to the client in the design and construction process. This influenced Johnston to view economic constraints as a challenge to be solved by inventiveness, instead of being a restriction on his artistry. During these years, Gilbert and Johnston kept in touch through a large number of letters.
In January 1880, Cass Gilbert departed to Europe for an architectural tour. Gilbert wrote back to Johnston urging him to make a similar trip, but Johnston was preoccupied with a job offer from Herter Brothers in New York. One of the projects on which he worked during his tenure at Herter Brothers was J.P. Morgan's brownstone house on Madison Avenue at 36th Street. In the summer of 1880, Cass Gilbert returned from Europe and settled in New York, working for the firm of McKim, Mead & White. Gilbert and Johnston, along with their MIT classmate Francis Bacon, shared rooms at 40 Irving Place. That same year Johnston, Gilbert, Bacon, Taylor, and William A. Bates founded the Sketch Club, which later became the Architectural League of New York. Accounts vary on which members were actually the founders of the club.
Clarence H. Johnston Sr.