Yes, Ireland is mentioned in numerous classical Roman sources.

In Geographica, (circa 7 BCE), Strabo describes it thus:

"Besides some small islands round about Britain, there is also a large island, Ierne, which stretches parallel to Britain on the north, its breadth being greater than its length. Concerning this island I have nothing certain to tell, except that its inhabitants are more savage than the Britons, since they are man-eaters as well as heavy eaters..."

He gets the location wrong, but it's true that Ireland has greater breadth (N-S dimension) than length (E-W dimension).

In Agricola, (circa 98 CE) Tacitus recounts the life of his titular father-in-law, who was governor of Britain. In his words;

"Ireland is small as compared to Britain, but it is larger than any of the Mediterranean islands. It resembles Britain in soil and climate, and in the character and customs of its inhabitants ; through trade and traders we are tolerably well acquainted with the approaches to it and with its harbours."

He also describes it as "lying between Britain and Spain and easily accessible from the sea of Gaul", which is not strictly accurate, but shows he at least knows roughly where it is.

In Geographia, (circa 150 CE) Ptolemy describes the location, outline, major rivers, tribes, and major settlements of the island (with coordinates!). Numerous reconstructions of his map exist; here is one that appears to be literally faithful to the text, with no artistic license taken. Obviously, it's not perfect, but the general sense of things is fairly accurate.

The overall impression I gather is that the Romans knew of the existence of Ireland before conquering Britain, though not with any great specificity, and after the conquest had significant trade and other contacts that advanced their knowledge considerably.