Beginning at the intersection of 4th Street N (US 92 and SR 687 and 5th Avenue N in St. Petersburg, Florida, it runs west of US 19 near the Gulf coast passing through the cities of Seminole, Clearwater, Dunedin and Tarpon Springs before ending at US 19 in Holiday, Pasco County, Florida. It is also the unsigned State Road 595 throughout the entire route. It also runs along much of the Pinellas Trail.
Alternate US 19 was established in 1951 when US 19 was realigned from St. Petersburg through Holiday. It hugs the Gulf coast, servicing Seminole, Clearwater, Dunedin and Tarpon Springs before ending at US 19 in Holiday. Originally, the southern terminus of US Alt 19 was at US 92/SR 687 in downtown St. Petersburg, but was truncated to US 19 in St. Petersburg.[when?]
As of September 2007, however, signage indicates that Alt US 19 once again follows US 19's old route all the way to US 92; this original route was numbered and signed as the hidden SR 595 designation of the main route, but the signs are slowly being phased out in favor of Alt US 19 shields. Both shields are in current use, however, for the time being, with the Alt US 19 signage on the highway itself, and the SR 595 directional signage at the intersections, including I-275 exit 23.
Prior to February 2007, Alt. US 19 originally went south through downtown Clearwater on Fort Harrison Avenue, which becomes Clearwater-Largo Road upon entering Largo. It then turned east along West Bay Drive to the intersection of Seminole Boulevard, then turned south. This intersection is also the western terminus of SR 686 and, until the reconfiguration, the southern terminus of SR 651.
As of February 2007, Alt. US 19 was realigned along Missouri Ave., directly north to SR 60 (Court/Chestnut Streets) in Clearwater, west to Myrtle Avenue, then north, before joining Fort Harrison Avenue south of Sunset Point Road. The new alignment now effectively bypasses the downtowns of Largo and Clearwater. The original alignment has since been decommissioned by the FDOT and downloaded to the cities of Largo and Clearwater. SR 651 still exists in FDOT's road inventory lists, but as a "hidden" route number along the new Alt. US 19 alignment.
When this plan was first announced in 2001, it was viewed as good news for commuters and businesses championing the project as a way to turn Clearwater into a walkable community.