The first Law Day, May 1, 1958, came about by Proclamation 3221 which President Dwight D. Eisenhower signed on February 3, 1958. The Proclamation read "The people of this nation should remember with pride and vigilantly guard the great heritage of liberty, justice, and equality under the law that our forefathers bequeathed us." A few years later, in 1961, Congress passed Pub. L. 87-20, 75 Stat. 43 establishing Law Day “for the cultivation of the respect for law that is so vital to the democratic way of life.”
The first of May was purposely chosen to contrast with May Day, a holiday which socialist nations celebrate on May 1 as International Workers Day in commemoration of the 1886 Haymarket riots in Chicago. The Brooklyn Law School Library has The Chicago Haymarket Conspiracy, and the Detection and Trial of the Conspirators through its subscription to HeinOnline.
This year, the American Bar Association has designated the theme for Law Day 2013 as “Realizing the Dream: Equality for All.” The ABA website lists themes for past Law Days. See the New York State Bar Assocation website for more on Law Day 2013.