In the late 1920s through 1931, today's Route 203 was called state highway 222.

The modern Route 222 was created from a mix of local and state roads in 1963. North Main Street in Thomaston was once part of Route 8. The southern portion of Hill Road is relatively new, created when the Thomaston Flood Control reservoir and dam were completed in 1960. A bill was introduced in Nov. 1960 to add this 2.6-mile road to the state highway system. Hill Road in Harwinton, from the Thomaston town line north to Route 118 was formerly SR 722: the origin of Route 222's eventual number.

• "Route 722 Bill To Be Introduced." Hartford Courant, Nov. 28, 1960.
• "Shanley Reports Relocated Roads Are Completed." Hartford Courant, Dec. 9, 1960.
• "Rudolph Diulio Resigns Post As Constable." Hartford Courant, Jan. 13, 1962. (Mentions 222 addition.)
• "8 Items of Business To Face Town Meeting." Hartford Courant, Oct. 2, 1964.

• Route 222 Ends (Photos; Doug Kerr at state-ends.com)
• Route 222 - Google Maps