Yes people were aware of him and he had support
The people of the Dunedain were indeed aware of his fostering in Rivendell as it was tradition for their Chieftains to be fostered there (Elrond did not take Aragorn but provided the traditional service of raising the future Cheiftain, having been aware of their lineage stretching back to his own brother, Elros), where the heirlooms of Isildur were kept:
Arahael his son was fostered in Rivendell, and so were all the sons of the chieftains after him; and there also were kept the heirlooms of their house: the ring of Barahir, the shards of Narsil, the star of Elendil, and the sceptre of Annúminas.
The Return of the King - Book 7, Appendix A: (iii) Eriador, Arnor, and the Heirs of Isildur
The Gondorians however, were unaware of the happenings in the North, and as far as the books lead us to believe were unaware of the Heirs of Isildur still existing. (As covered in this Q&A)
Had Aragorn chosen to announce his kingship after coming of age, he would've had support from the Dunedain as he was the Chieftain of that people. However, as covered in this Q&A, an earlier return by Aragorn would've led to the rejection from the people of Gondor, the largest population of Men and the most powerful, and as such he would've been cast aside, as Arvedui had been before him.