Cooley, Thomas McIntyre (6 Jan. 1824-12 Sept. 1898), jurist, was born in Genesee County, New York, the son of Thomas Cooley and Rachel Hubbard, farmers. Thomas grew up in the "Burned-Over" district of western New York at a time of religious revivals and anti-Masonic and Whig political ferment. As a young man he appears to have shared his parents' equal-rights Jacksonianism, their "Jeffersonian bias" as one of his friends later wrote. Cooley attended Attica Academy and was inclined to literary interests and the law, although previous generations of Cooleys had been farmers. In 1842 he studied law with Theron Strong, a former Democratic congressman, in Palmyra, New York. In 1843 he went to Michigan, where he settled in Adrian and continued to read law in local offices. He was admitted to the bar in 1846 and married Mary Horton that same year; they had six children. At mid-century Cooley's small legal practice was complemented by literary, journalistic, and political interests. He wrote poems attacking war and slavery and celebrating the European revolutions of 1848. He edited Democratic newspapers and acquired a reputation as a "Progressive Democrat." He also helped organize the Free Soil party in Michigan in 1848 and became a Republican in 1856.

In the 1850s Cooley concentrated more narrowly on the law and began to gain professional recognition. He served as compiler of Michigan statutes, as reporter to the state Supreme Court, and in 1859 became one of the first professors of law at the University of Michigan. He moved from Adrian to Ann Arbor in 1859 and remained there for the rest of his life as an important leader of the community and of the developing University of Michigan. In 1864 he was elected to the Michigan Supreme Court, where he served as the leading justice for twenty years. He was an independent Republican but considered running for Congress as a Liberal Republican in 1872. As a Mugwump he supported Grover Cleveland in 1884 and again in 1892. His independence may have cost him an appointment to the U.S. Supreme Court, but it also contributed to his 1887 nomination by President Cleveland to the Interstate Commerce Commission, where he emerged as the dominant commissioner. Henry Carter Adams, the young Michigan political economist whom Cooley brought to the commission as its chief statistician, wrote that Cooley's resignation, for health reasons, "was a national calamity." Adams believed that Cooley had begun to develop the meaning of the Interstate Commerce Act by administrative interpretation in the same way that John Marshall had developed the meaning of the Constitution. Ironically, the U.S. Supreme Court in the 1890s was not receptive to Cooley's ideas of administrative law.

In 1868 Cooley's Treatise on the Constitutional Limitations Which Rest upon the Legislative Power of the States of the American Union was published. The book went through six editions by 1890 and was probably the best-known legal treatise in the late nineteenth century. Cooley called it a mere "attorney's companion," but it was more than that. Published as the Fourteenth Amendment was being ratified, the treatise, especially Cooley's chapter on the protection of property by the "due process" clause of state constitutions, gained immediate attention because of its substantive, rather than mere procedural, definition of due process. For Cooley, due process meant that the powers of government must be exercised in accord with the "settled maxims" of the common law, especially its safeguards for the protection of individual rights. Cooley's common-law constitutionalism also protected individual liberty from arbitrary regulations that restricted rights "in a manner before unknown to the law." "Established principles," not mere procedure, determined whether a legislative or administrative act was due process.

At a time when American corporations began to look to the courts for protection against legislative regulation, Cooley's restrictive views of due process as based on common law maxims and Jacksonian views of "equal liberty" were regarded by some jurists as justification for "laissez-faire" policies. But Cooley did not intend to offer a constitutional refuge for corporations or unrestrained economic activity. His treatise accepted a broad police power and expressed skepticism of judicial review, a skepticism shared by James Bradley Thayer's criticism of that doctrine. On the Michigan court Cooley denied that due process meant judicial process (Weimer v. Bunbury. 30 Mich. 203 [1874]), and when he was on the Interstate Commerce Commission he defended administrative rate-setting against court decisions that said such actions violated due process. Cooley's commitment to individual rights did not extend to a defense of corporate rights. In several decisions on the Michigan court Cooley attacked the Dartmouth College case and its protection of corporate charters (East Saginaw Manufacturing Company v. The City of East Saginaw, 10 Mich. 274 [1869]).

He acquired some notoriety with his 1870 opinion in People v. Salem (20 Mich. 487), which denied tax aid to private railroad corporations because such aid served no "public purpose" and was "class legislation," inconsistent with the doctrine of "equal rights."
Cooley published articles for the leading journals of the day and was in demand as a lecturer to bar associations and as an arbitrator of trunk-line disputes. Work became something of a narcotic for him, as one of his children said, and in the 1880s overwork contributed to his deteriorating health. Ambivalence, created by his commitment to principles of both equality and liberty, inclined him to a nostalgic conservatism at odds with the political corruption, the concentration of wealth, and the conflict of labor and capital in post-Civil War America. His anxiety was evident in an 1879 lecture on city government in which he remarked that "poverty was never in so much danger of becoming master as when capital unjustly manipulates the legislation of the country."

Cooley enjoyed a close family life in Ann Arbor and was desolate after his wife's death in 1890. His health continued to decline, and, according to his physician son, Thomas, his death in Ann Arbor came as a "long-delayed and much-hoped-for release."

His son Charles Cooley, who became a noted sociologist, believed that his father's life had been narrowed by the ideology of the law and that "a nature susceptible and warm enough at the start has been confined by a one-sided development." That may be the case, but Cooley's predicament was also an ironic commentary on tensions between politics and the law and between equality and liberty in American life.