The Earliest counter-Earth in American radio was probably Krypton. Krypton was and is usually described as an exoplanet in another star system.
But the radio program The Adventures of Superman (1940-1951) described Krypton as a counter-Earth beginning on February 1940. In the first few episodes Krypton was destroyed and Superman journeyed to Earth.
In the American TV series The Adventures of Superman (1952-1958) the first episode showed the destruction of Krypton and Superman travelling to Earth. The narrator describes Krypton as being "millions of miles" from Earth, which is literally consistent with it being a counter-Earth.
If Krypton was not depicted as a counter-Earth the first in an American science fiction TV program might have been Olympus in the animated Sport Billy, produced by Filmation in the USA but first broadcast in Europe in 1980 before being shown in the USA in 1982.
The first counter-Earth in American comic strips was probably Terra in Twin Earths which rain as a daily strip from June 16, 1952 to May 25, 1963 and a Sunday strip from March 1, 1953 to December 28, 1958.
The first counter-Earth in an American novel I could find was in Planetoid 127 by Edgar Wallace in 1924 (but user 14111 seems to have found an 1896 example as in his accepted answer). John Norman could have read about a counter-Earth in Ben Barzman's 1960 novel Out of This World, also known as Twinkle Twinkle Little Star, also known as Echo X.