Treat Baldwin Johnson (29 March 1875 – 28 July 1947) was an American organic chemist and Sterling Professor at Yale University from 1928–1943.

In 1918, he received the Nichols Medal of the American Chemical Society in recognition of his work on pyrimidines.

[1]: 83 Johnson supervised 94 graduate students, together generating 182 papers on pyrimidine chemistry in a total research output of 358 publications and 15 patents.

[4] He was the co-editor with E. M. Shelton, one of his students, of the owner's manual for A. C. Gilbert Company's chemistry sets.

[5] Together with R. D. Coghill, Johnson was the first to discover the existence of 5-methylcytosine in nature, from tuberculinic acid, a nucleotide of Mycobacterium tuberculosis.