The 33-year-old takes charge after Owen Coyle resigned from his position with immediate effect on Thursday evening.
The former Burnley and Blackburn Rovers manager quit with his side rooted to the bottom of the Ladbrokes Premiership table.
Kettlewell, a former County midfielder, had previously been in charge of the club’s Development League side.
His first match will likely come next weekend after Saturday’s clash with Partick Thistle was postponed.
The crucial clash between the two clubs currently residing in the relegation spots became the latest top flight fixture to fall victim to the weather.