The counties covered by the declaration are Bastrop, Burnet, Colorado, Fayette, Hood, Jim Wells, Kerr, Kimble, La Salle, Live Oak, Llano, Mason, McMullen, Nueces, Real, San Patricio, Travis and Williamson.
Water levels are quickly dropping on a Texas river that soared above flood stage this week, destroying a bridge, forcing evacuations and leading to multiple water rescues. The National Weather Service says both rivers are experiencing "major flooding" following several days of rain.
Officials say there's a continued threat for flooding in Central Texas as more rain is expected to fall on the already saturated area and dams along the swollen Colorado River release some of the flood downstream.
More rain is forecast for Wednesday and Thursday and flood warnings remain in place for large parts of Texas.
The Llano River's crest of 39.91 feet in Llano was just below the record high of 41.5 feet there in June 1935.
Authorities said it does not to appear to be a person missing from the South Llano River flooding in Junction more than a week ago. Three bodies have been recovered.
The rain also was causing problems in other parts of Texas. At least one fatality is suspected to have been caused by the flooding; local news reported a body had been found "related to the flooding".
The Fort Worth Fire Department said it responded to some 80 traffic accidents blamed on slick roads and poor visibility Tuesday morning.
Torrential rain has fallen across central Texas for two days with Llano County being deluged by 30.5cm (12 inches) of water. It was just after 9:00 a.m. when the FM 2900 bridge in Kingsland collapsed, sending chunks rushing down the river.