SR 9 was created from several previously constructed roads. One of these was a toll road built in 1848 by
Martin McCarty, from near the Santa Cruz Mountains summit to Saratoga. The section from Santa Cruz to Felton also operated as a toll road, from its construction in 1860 to 1872. The Toll House, built in 1867, remains next to the highway. In 1913, the road from
Saratoga Gap southwest to
Big Basin Redwoods State Park via the present SR 9 and
SR 236 was added to the state highway system; it became
Route 42 (an unsigned designation) in 1917. Although this highway connected to
Route 44, the remainder of present SR 236, the only connection to the continuous state highway system was with the
Skyline Boulevard (
Route 55, now
SR 35) at Saratoga Gap. This changed in 1933, when Route 42 was extended east from the gap to
Route 5 (
SR 17) in
Los Gatos, and a new
Route 116 was created, running south from Route 42 at
Waterman Gap (about halfway between Saratoga Gap and the park) to
Santa Cruz, intersecting the end of Route 44 at
Boulder Creek.
Sign Route 9 was marked in 1934; however, it did not entirely follow the present SR 9. Initially it connected Santa Cruz with
Milpitas, following Routes 116 and 42 to
Saratoga,
Route 114 (Saratoga Sunnyvale Road and Mathilda Avenue) north through
Sunnyvale, and
Route 113 (
SR 237) east to
Route 5 (Main Street, then
U.S. Route 101E and
Sign Route 13) in Milpitas. When the
San Jose-
Oakland US 101E designation was dropped in the mid-1930s, Route 5 between
Mission San Jose (where the new
SR 21 turned northeast) and
Hayward did not retain a signed designation. Later SR 9 was extended north along
SR 17 (which had replaced SR 13) from Milpitas to
Warm Springs, SR 21 to Mission San Jose, and the independent section of former US 101E—all part of Route 5—to
US 50 (also Route 5, which included a branch to Oakland) near Hayward. Except for a short realignment in the mid-1950s onto
Route 69 (now
I-880 and
SR 262) between Milpitas and Warm Springs, this alignment remained until the
1964 renumbering. In 1964, SR 9 was moved to its present alignment, taking over the previously unsigned Route 42 from Saratoga to Los Gatos. The route that had been signed as SR 9 became
SR 85 through Sunnyvale,
SR 237 to Milpitas (including previously unsigned extensions of Route 113 at each end), part of
SR 17 through Warm Springs,
SR 262 through Warm Springs, part of
I-680 to Mission San Jose, and
SR 238 from Mission San Jose to Hayward (SR 21 was already renumbered I-680 by then). SR 85's original designation was deleted in 1994 and has since moved to a
freeway and SR 17 in Warm Springs was renumbered I-880 a decade prior. However, the SR 237 freeway was built in the same location, and both SR 238 and most of SR 262 remain as surface roads. ==Major intersections==