Leicestershire lost opener Darren Maddy and Aftab Habib early but Mongia and John Maunders (71) spoiled their party and put on 91 runs for the third wicket to lay the foundation for a big total.
John Saddler (47) was giving company to Mongia at stumps.
Even though it was not easy to play the strokes on this kind of wicket and patience was the key, Mongia showed tremendous application and mixed caution with aggression and despite rival captain bring in frequent bowling changes, Mongia was rock solid and the exercises proved futile.
Coming off a knock of 165 against Essex, Mongia once again showed his class and reached his century off 193 balls with 11 fours and was seen celebrating it with a six off Croft that soared over extra-cover.
In the end, Mongia was batting on 142 off 273 balls which included 13 hits to fence, besides that six and shared an unbroken fourth-wicket stand of 155 with a dour Saddler.
In another Division Two County Championship match, Zaheer Khan's Worcestershire meet Derbyshire at home later today.