We report a search for a magnetic monopole component of the cosmic-ray flux in a 2743-live-day exposure of the NOvA experiment’s Far Detector, a 14,kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of $8\times {10}^{-16}c{m}^{-2}{s}^{-1}s{r}^{-1}$ at 90% C.L. for monopole speed $6\times {10}^{-4}<\beta <5\times {10}^{-3}$ and mass greater than ${10}^9$,GeV. Because of NOvA’s small overburden of 3~meters-water equivalent, this constraint covers a previously unexplored low-mass region.