Eternity, Eternity, That boundless, &c. J. Montgomery. [Eternity.] In the M.MSS. this hymn is dated, "The Mount, December 20,1836" (the "Mount" was his Sheffield residence), but it did not appear in print, so far as has been traced, until his Original Hymns, 1853, where it is given as No. 238 in 4 stanzas of 4 lines, and headed with a line of one of his most popular hymns, "Forever with the Lord."
--John Julian, Dictionary of Hymnology (1907)