The [First] Book of Urizen, with a publication date of 1794, was the most elaborate illuminated book Blake had yet produced. It consists of 28 plates, all of them with illustrations, 10 of them full page illustrations with no text. There are eight known copies of the poem, copies A through G and J, as well as a number of separate unbound pages. Copies A and B have all 28 plates; the other copies are missing one or more plates. The sequence of the plates with text on them is determined by the text, but the 10 plates with full page illustrations vary in their placement. Plate 4 with 71 lines of poetry is missing from copies D-G and J.
I am following David Erdman's sequence of plates. Although it lacks Plates 4 and 16, Copy D offers the basic sequence of the text. The placement of Plate 4 is determined by the text. The placement of Plate 16, a full page illustration, is more open to interpretation. Of the three copies that have Plate 16, Copies A and B place it after Plate 15; Copy G places it after Plate 11. The fact that Copy G was printed at a considerably later date adds to the authority of the placement of the Plate in A and B as being closer to Blake's original intentions. Copy G is printed on paper with an 1815 or 1818 watermark; the other copies are printed on paper with a 1794 watermark (except A with no watermark). See Erdman (Complete 804 and Illuminated 182), Bentley (166-85), and Worrall (148-49) for discussions of the different copies of the book and of the sequence of the plates.