This street was named for Alonzo Hamblet (1863–1937), son of Eli (1820–1905) and Mary Booth Hamblet (1840–1905), namesake of Mary Avenue NW. According to an article in the November 19, 1937 issue of The Seattle Times, the Hamblets had their homestead where Ballard High School is today. Alonzo was one of the men behind the West Coast Improvement Company that developed Ballard (then known as Gilman Park).

Alonzo Avenue NW begins at NW 67th Street just north of the high school and goes ⅖ of a mile to NW 75th Street.

Street sign at NW 67th Street and Alonzo Avenue NW, Seattle, October 12, 2021
Street sign at NW 67th Street and Alonzo Avenue NW, Seattle. Photograph by Benjamin Lukoff, October 12, 2021. Copyright © 2021 Benjamin Lukoff. All rights reserved.