Air carrier First Officer reported putting 'NOONE' instead of the correct 'NOONN' into the FMS and the mistake was not caught until ATC questioned and informed the flight crew the flight was south of course; which led to the flight crew reviewing the flight plan and finding the error.

Narrative

Normal procedures first flight of the day XNA to ZZZ. AOM and FOM procedures followed. No rushing or fatigue applicable. I was PF and after completing the normal first flight of the day flows and walk around; I entered the cleared route of flight into the FMS. CA and I reviewed the flight plan per the FOM. He read the FMS and I reviewed the points using the clearance as well as the Jepps chart routing for the flight. All points checked when reviewed verbally (phonetically) and the flight distance was within a reasonable distance of the planned routing. However; once in flight we crossed BETIE and within a few miles ATC inquired if 'we were direct to NOONN' to which we replied yes. The controller stated that we were slightly south of course. We reviewed the FMS and discovered that I had incorrectly entered 'NOONE' instead of 'NOONN' and it was not caught during the flight plan review. NOONE and NOONN are 111 NM apart further complicating the ability to catch the mistake during route review using the flight distance. ATC cleared us direct to COMDY (the next fix after NOONN) and the flight continued to the destination without event. ATC did not issue any brasher or pilot deviation warnings.Cause: FO's incorrect route entry misspelling 'NOONE' instead of 'NOONN.' Additionally contributing; CA and FO's failure to catch the misspelling during the route review. Further contributing to the cause was the fairly close proximity of fix 'NOONE' and 'NOONN'.Suggestions: Pilot reading the FMS route verification should also verify spelling of fixes cross-checked to the PDC and or Jepps chart to verify any spelling errors. Additionally; pilots can also use the FMS map plan page and review the physical route of flight and compare it to the Jepps routing.