The Volokh Conspiracy
Mostly law professors | Sometimes contrarian | Often libertarian | Always independent
Each of the 13 federal circuit courts of appeals gets a Justice assigned to it, mainly to handle one-Justice applications (for stays, extensions of time, and the like) coming from that Circuit.
They are often given to Justices based on their connections to the circuit. Several Justices have the circuits on which they hard served: Roberts (D.C.), Sotomayor (2d), Alito (3d), Barrett (7th), Gorsuch (10th). Justice Thomas has the 11th, presumably because he's from Georgia. Naturally, some Justices have to double up (and Chief Justice Roberts is quadrupling up, though three of his circuits are the ones with the smallest caseloads).