State Road 688 (SR 688) is an east–west route in Pinellas County running from Indian Rocks Beach to northeastern St. Petersburg, Florida, where it merges onto Interstate 275 (I-275).

The highway changes its name as it heads east across Pinellas County.

It skirts Largo before crossing U.S. Route 19 (US 19) and then merges briefly with Roosevelt Boulevard (SR 686).

Ulmerton Road was named for the community of Ulmers, which arose around Marion Ulmer's turpentine still, timber and naval stores interests in the first half of the twentieth century.

Today it carries traffic across the middle of the most densely populated county in Florida.