It seems that Adam was created in grace. Some have said that Adam was created without grace but only in a state of nature and that this state was strictly meritorious. Thomas Aquinas shows that the first man was created in grace:

But the very rectitude of the primitive state, wherewith man was endowed by God, seems to require that, as others say, he was created in grace, according to Ecclesiastes 7:30, “God made man right.” For this rectitude consisted in his reason being subject to God, the lower powers to reason, and the body to the soul: and the first subjection was the cause of both the second and the third; since while reason was subject to God, the lower powers remained subject to reason, as Augustine says [Cf. De Civ. Dei xiii, 13; De Pecc. Merit. et Remiss. i, 16.]

Now it is clear that such a subjection of the body to the soul and of the lower powers to reason, was not from nature; otherwise it would have remained after sin; since even in the demons the natural gifts remained after sin, as Dionysius declared (Div. Nom. iv). Hence it is clear that also the primitive subjection by virtue of which reason was subject to God, was not a merely natural gift, but a supernatural endowment of grace; for it is not possible that the effect should be of greater efficiency than the cause. Hence Augustine says (De Civ. Dei xiii, 13) that, “as soon as they disobeyed the Divine command, and forfeited Divine grace, they were ashamed of their nakedness, for they felt the impulse of disobedience in the flesh, as though it were a punishment corresponding to their own disobedience.” Hence if the loss of grace dissolved the obedience of the flesh to the soul, we may gather that the inferior powers were subjected to the soul through grace existing therein.

Summa theologiae Ia, q. 95, a. 1

Thomas argues that the results of the fall prove that Adam fell from grace. Otherwise, Adam would have fallen from nature, which is impossible.