All Executive Orders and Proclamations issued after March 1936 are required by law to be published in the Federal Register. These Executive Orders and Proclamations are then published in Title 3 of the Code of Federal Regulations.
For Executive Orders before 1936, use the Congressional Information Service’s Presidential Orders and Proclamations. This resource and its attendant Index can be used to quickly track down Executive Orders issued from 1789 to 1980 by subject and number, or date.
Other helpful collections include:
Executive Orders were unnumbered until 1907, when the Department of State started assigning numbers. However, many Executive Orders were not deposited with the Department of State and were instead kept in the agency to which they pertained. Some appear to have been lost.
The passage of the Federal Register Act in 1936 required Executive Orders to be published in the Federal Register, and the Division of the Federal Register (now Office of the Federal Register) began numbering consecutively from that time forward. Due to the inconsistent numbering and retention of Executive Orders before the late 1930s, it is practically impossible to determine exactly how many Executive Orders were produced by each president before Truman.