The delegates to the Washington Constitutional Convention drew on many sources, including the federal constitution, constitutions from other states, and constitutions that were drafted for Washington in 1878 and 1889 (before the Convention).
Quentin Shipley Smith's notes in the Journal cited many of these sources.
Another useful tool is Arthur S. Beardsley, Sources of the Washington Constitution, in State of Washington, 2011-2012 Legislative Manual at 385-422. Beardsley first prepared this study comparing provisions of the Washington State constitution with parallels in the federal constitution, other state constitutions, and the Hill and 1878 draft constitutions in 1939. It is reprinted every two years in the Legislative Manual. The link above is to the Legislative Manual on the legislature's website. For a smaller file, with just Beardsley's work, click here.
Links to the Washington sources and state and federal sources follow.
Washington Constitution, 1878 (Washington Secretary of State). This links to a digital image of the original handwritten text. For a typeset version, see Meany & Condon. The 1878 constitution was drafted by a constitutional convention held in Walla Walla and approved by the voters, but lacked congressional authorization. See discussion here.
Edmond S. Meany & John T. Condon eds., Washington's First Constitution, 1878, and Proceedings of the Convention (1924?). The text of the constitution is reprinted at pages 63-104. Originally published in 9 Wash. Hist. Q. 129-52, 208-229, 296-307 (1918)
Hill Constitution: William Lair Hill, A Constitution Adapted to the Coming State: Suggestions by Hon. W. Lair Hill: Main Features Considered in Light of Modern Experience: Outline and Comment Together. 1889. (This document is an undated typescript. Hill's proposed constitution was also published in The Morning Oregonian, July 4, 1889, here, here, and here.)
Enabling Act, ch. 180, 25 Stat. 676 (1889)*** ("An act to provide for the division of Dakota into two States and to enable, the people of North Dakota, South Dakota, Montana, and Washington to form constitutions and State governments and to be admitted into the Union on an equal footing with the original States, and to make donations of public lands to such States."). The Enabling Act is also reprinted in State of Washington, 2011-2012 Legislative Manual at 33-51; this version includes amendments to section 11, which concerns public lands granted for school purposes, in 1921, 1932, 1938, 1948, 1952, 1962, 1967, and 1970.
Rules of the Constitutional Convention of the Territory of Washington, July 4, 1889. This pamphlet was published for the use of the delegates. It contains the report of the Rules Committee with the rules adopted by the convention; the report and rules are also found in the Journal, at 21-33. Pages 8-9 of the pamphlet list the convention's standing committees and their members; these are also found in the Journal, at 19-20 and 37.
Alabama Constitution, 1868 (Alabama legislature)
Arkansas Constitution, 1874 (Google Books)
California Constitution, 1879 (California Secretary of State)
Colorado Constitution, 1876 (Colorado State Archives)
Declaration of Independence (National Archives)
Illinois Constitution, 1870 (Google Books)
Indiana Constitution,1851 (Indiana Historical Bureau)
Iowa Constitution, 1846 (Google Books)
Iowa Constitution, 1857 (State Library of Iowa)
Kansas Constitution, 1859 (Kansas Historical Society)
Maryland Constitution, 1867 (Maryland State Archives)
Minnesota Constitution, 1857 (Minnesota Historical Society)
Nevada Constitution, 1864 (pp. 833-55 of Official Report of the Debates and Proceedings of the Constitutional Convention of the State of Nevada Assembled at Carson City to Form a Constitution and State Government (1866)
New Hampshire Constitution, 1792 (Google Books)
New York Constitution, 1846 (pp. 72-94 of The Constitution of the State of New York, with Notes, References and Annotations (Robert C. Cumming et al. eds., 1894)
Ohio Constitution, 1851 (Ohio Historical Society)
Oregon Constitution, 1857 (Oregon State Archives).
Texas Constitution, 1876 (University of Texas Tarlton Law Library)
Wisconsin Constitution, 1848 (Wisconsin Historical Society)
Constitutions of the United States, National and State (2d ed. 1974-). 6-volume looseleaf, regularly updated. Current volumes KF4530.C65 1974 at Reference Area; superseded pamphlets KF4530.C65 1974 at Compact Stacks.Catalog record.
Ronald K. L. Collins, Bills and Declarations of Rights Digest, in The American Bench: Judges of the Nation 2483-2655 (3d ed. 1985/86)** (includes text of all states' bills and declarations of rights, as well as notes and comparative tables).
George A. Glynn, American Constitutions, comprising the Declaration of Independence, the Articles of Confederation, the Constitution of the United States, and the State Constitutions (Albany: Argus, 1894) (the convention manual for the sixth New York State constitutional convention). Google Books: vol. 1, vol. 2. Catalog record.
Benjamin Hough, American Constitutions: Comprising the Constitution of Each State in the Union, and of the United States, with the Declaration of Independence and Articles of Confederation; Each Accompanied by a Historical Introduction and Notes, . . ., 2 v. (Albany: Weed, Parsons & Co., 1871-1872). HeinOnline link (UW restricted). Google Books: Vol. 1, Vol. 2
Benjamin Perley Poore,
William Finley Swindler, Sources and Documents of American Constitutions (v. 1-11, published 1973-79), KF4530 .S94 at Classified Stacks
William Finley Swindler, Sources and Documents of American Constitutions, 2nd Series (v. 1-5, published 1982-87), KF4530 .S94 at Classified Stacks
Francis Newton Thorpe, ed., The Federal and State Constitutions, Colonial Charters, and Other Organic Laws of the States, Territories, and Colonies Now or Heretofore the United States of America (GPO, 1909). HeinOnline (UW restricted). JK18 1909 at Classified Stacks.
John Joseph Wallis, NBER/University of Maryland State Constitution Project. Project is "a portal to the texts of the state constitutions of the United States. There have been almost 150 state constitutions, they have been amended roughly 12,000 times, and the text of the constitutions and their amendments comprises about 15,000 pages of text." Prof. Wallis states that this collection is more accurate than those by Poore, Thorpe, and Swindler. It much more current, since it includes changes through 2000.