The spell Etherealness reads in part:
You step into the border regions of the Ethereal Plane, in the area where it overlaps with your current plane. […] You can see and hear the plane you originated from, but everything there looks gray, and you can't see anything more than 60 feet away.
While on the Ethereal Plane, you can only affect and be affected by other creatures on that plane. Creatures that aren't on the Ethereal Plane can't perceive you and can't interact with you, unless a Special ability or magic has given them the ability to do so.
It's not clear to me whether or not Locate Object satisfies the qualifications of the second paragraph.
By extension, it seems like this spell's description includes a little general description about the ethereal plane. This would mean that the second paragraph applies both to the spell Etherealness and to creature abilities like Night Hag's Etherealness.
The confusion for me results from how the Ethereal plane intersects with other planes, suggesting that they are congruent from at least a spacial sense. For example, Blink states:
While on the Ethereal Plane, you can see and hear the plane you originated from, which is cast in Shades of Gray, and you can't see anything more than 60 feet away.
This suggests that distance measurements ignore planar considerations.
Given this, does the spell Locate Object work to detect an object (carried by a creature using the spell or ability above) if that creature and object are located within 1,000 feet but on the ethereal plane?
Best Answer
This question essentially boils down to defining the distance between planes and that matter has been addressed already in this question.
To wit, there is no standard definition of interplanar distance in the game, though certain spells address the matter on a case-by-case basis for their own purposes.
While Locate Object is magical, which would seem to indicate that it satisfies Etherealness' clause stating "unless a Special ability or magic has given them the ability to do so," the fact is that Locate Object does not expressly grant detection across/between planes.
Therefore, because spells only do what they say they do (and nothing more nor less), we have to conclude that Locate Object does not grant its caster the ability to detect across planes.