Originally part of Guess Road, North Buchanan Boulevard extended north from West Main Street; there was no South Buchanan Boulevard until the 1960s. The road was later called Guess Street (following a typical pattern of the 'in-town' portion being named ... Street, and the out of town portion ... Road.)
There are a number of Buchanans around from whom the name could derive; James Buchanan Duke is the most likely, though unconfirmed.
North Buchanan Boulevard continues into Guess Road north of West Club Blvd. However, there is a small section of N. Buchanan that exists north of I-85 as well, between 85 and Leon Street.