Abstract: The NASA Transiting Exoplanet Survey Satellite (TESS) mission will discover thousands of candidate transiting exoplanets.  Due to the mission configuration, 74% of the area to be observed by TESS will only have an observational baseline of 27 days. For those planets with orbital periods longer than 13.5 days, TESS can only capture one or two transits, which means the true ephemerides will be difficult to determine from TESS data alone. Follow-up observations of the transits of these candidates to confirm and characterize them will require precise ephemerides.  We explore the value of using existing ground-based wide-field photometric surveys to constrain the ephemerides of the TESS single-transit candidates.  The Kilodegree Extremely Little Transit (KELT) survey has a long observation baseline (up to ten years) and monitors fields that largely overlap with the TESS footprint, and also observes stars of similar brightness.  We insert simulated TESS-detected single transits into KELT light curves, and evaluate how well their orbital periods can be recovered.  We find that KELT photometry can be used to confirm ephemerides with high accuracy for planets of Saturns size or larger with orbital periods as long as a year, and therefore span a wide range of planet equilibrium temperatures.  In a large fraction of the sky we recover 20% to 50% of the warm Jupiter systems (planet radius of 0.9 to 1.1 R_J and 13.5<P<60 days), 35% to 75% of the warm inflated Jupiters (planet radius of 1.1 to 2 R_J), 3% to 13% of the temperate Jupiters (60<P<300 days), 7% to 40% of the temperate inflated Jupiters and 8% to 30% of the warm Saturns (planet radius of 0.5 to 0.9 R_J and 13.5<P<60 days).  The resulting periods and ephemerides of the signals can then be used by follow-up teams, whether part of the TESS mission or the community-organized ExoFOP-TESS project, to plan and coordinate follow-up observations to confirm candidates as planets, eclipsing binaries, or other false positives, as well as to conduct detailed transit observations with facilities like JWST or HST.