@BobJacobsen's comment about the MX Missile (and protests) in the 1980's got me clicking in Wikipedia, which led me to the Minotaur IV launches, the most recent of which seems to be ORS-5 or "SensorSat", a roughly 140 kg spacecraft built my MIT to "keep an eye on GEO".
Ran in a 5-stage configuration, using an extra Orion 38 motor to put ORS-5 in to an equatorial orbit.
This configuration would have normally been four stages, the additional stage was needed for the delta-v to make a plane change equatorial LEO.
It turns out I've asked a previous question about this launch: What inclination change could the 5th stage Orion 38 motor provide ORS-5 (SensorSat)?:
The screen shot and block quote below are from Orbital ATK's Mission Update: Minotaur IV ORS-5 Launch. ORS-5 or "SensorSat" is a technology demonstration for a class of satellites that will sit in LEO and keep an eye on the GEO belt for any "debris" which I suspect means pranksats or worse. ORS-5 will sit in a 600 x 600 km equatorial LEO.
See that question and the answer there for several more links.
Question: In the 21st century or thereabouts, how often are five stages used to put a relatively light spacecraft into low Earth orbit? Even for a heavy payload, is it quite rare to use five distinct stages to LEO?