  A small fraction of gamma-ray bursts (GRBs) exhibit blackbody emission in the
X-ray spectra, the origin of which is debated. In order to gain a more complete
understanding of this phenomenon, we present a search for blackbody components
in 116 GRBs with known redshifts observed by {\it Swift}~XRT. A time-resolved
spectral analysis is carried out and the significance of the blackbody is
assessed with respect to an absorbed power-law model. We report nine new
detections and confirm the previously reported blackbody in GRB~171205A.
Together with our previous results, there are a total of 19 GRBs with
significant blackbody emission in a sample of 199 GRBs observed by {\it Swift}
over 13 years. The detections include one short GRB and two low-luminosity
GRBs. We estimate fireball parameters from the blackbody components and note
that the blackbody luminosity is correlated with the temperature and inferred
Lorentz factor. There is a large spread in the properties of the blackbody
components and the light curves, which points to different origins for the
emission. In about a third of the GRBs, the blackbody is clearly associated
with late prompt emission from the jet. The rest of the sample includes cases
that are fully consistent with the expectations from a cocoon, as well cases
that may be explained by high-latitude emission or more energetic cocoons.
These results indicate that thermal emission is associated with all parts of
the jet.
