Ohio’s abbreviation used to be just “O.”

Ohio welcome sign

With the 1831 publication of Table of the Post Offices in the United States, the Post Office Department acknowledged the population’s reluctance to completely spell out state names on mailing envelopes (such as the always-vexing “Massachusetts”) and for the first time unveiled a list of approved abbreviations. The list largely followed consistent guidelines: States with one-word names were abbreviated with their first and last letters (e.g., Connecticut became “Ct.”); states with two-word names were marked by their initials (New York became “N. Y.”); and territories were shortened to two letters with a “T” (Arkansas Territory became “Ar. T.”). But there were a few anomalies among the group: Alabama and Illinois were denoted by their first two letters (“Al.” and “Il.”); Michigan Territory retained its first three (“Mic. T.”); Missouri used a middle letter (“Mo.”) to avoid confusion with Mississippi (“Mi.”); and Ohio simply became “O.”

When the U.S. Post Office released updated lists in 1874 and 1943 to account for the country’s expansion, it did away with abbreviations for Ohio and other states with short names. Then, in mid-1963, the department established new two- to four-letter abbreviations for all states — with the exception of Ohio, Iowa, and Utah — to fit the templates of new mail processing equipment. When the four-letter designations were still found to be too long, the Post Office shortened them one more time in October 1963 to a consistent two letters, and Ohio, Iowa, and Utah became “OH,” “IA,” and “UT.” And that’s where things stand today. The only state abbreviation that has changed since 1963 is Nebraska‘s; originally given the two-letter abbreviation of “NB,” the Cornhusker State was rebranded as “NE” in 1969 to avoid confusion with the Canadian province of New Brunswick.

By the Numbers

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The Post Office introduced a mascot to promote the use of ZIP codes.

When mail services struggled to keep pace with America's booming population after World War II, the Post Office Department sought to streamline the process by dividing the country into regions marked by five-digit Zone Improvement Plan (ZIP) codes. However, the department had taken note of the recent pushback against the introduction of area codes for the telephone, so it introduced a cartoon mailman named Mr. Zip to help persuade the public to add these five numbers to outgoing mail. Mr. Zip was initially featured on Post Office promotional materials, mail trucks, and buttons worn by carriers; he also appeared in a 1967 PSA alongside a band that performed ZIP code-themed songs and skits. When ZIP code usage continued to lag, he found his way onto kids' lunch boxes, a board game, and into a Dick Tracy cartoon. It's unclear just how effective Mr. Zip was as a pitchman, but the relentless promotional push led to nearly 100% of Americans adopting the ZIP code by the late 1970s, and allowed the Postal Service to ease the smiling mailman into retirement in 1983.