This episode takes place in Baltimore, Maryland on February 21, 1861 and in Arizona in 1968.
Allan Pinkerton actually did foil an assassination plot while Abraham Lincoln was en route from Baltimore to Washington, D.C. for his inauguration in February 1861. Pinkerton's agency solved a series of train robberies during the 1850s, first bringing Pinkerton into contact with George McClellan, then Chief Engineer and Vice President of the Illinois Central Railroad, and Abraham Lincoln, the company's lawyer.
Ford Rainey, who plays President Abraham Lincoln, previously played President Henry Talbot McNeal in Irwin Allen's Hot Line (1964) and Doomsday (1965), and an unnamed US President in Allen's No Place to Hide (1965)/The Reluctant Stowaway (1965).
In 1861 Baltimore, Maryland, where this episode takes place, had a population of about 215,000 and was the fourth largest city in the United States.
Baltimore, Maryland is located 38 miles northeast of Washington, D.C.