Jacobson v Massachusetts, a 1905 US Supreme Court decision, raised questions about the power of state government to protect the public’s health and the Constitution’s protection of personal liberty. We examined conceptions about state power and personal liberty in Jacobson and later cases that expanded, superseded, or even ignored those ideas.Public health and constitutional law have evolved to better protect both health and human rights. States’ sovereign power to make laws of all kinds has not changed in the past century. What has changed is the Court’s recognition of the importance of individual liberty and how it limits that power. Preserving the public’s health in the 21st century requires preserving respect for personal liberty.