  We present the source associations, cross-identifications, and
multi-wavelength properties of the faint radio source population detected in
the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields.
The first LoTSS Deep Fields data release consists of deep radio imaging at
150~MHz of the ELAIS-N1, Lockman Hole, and Bo\"{o}tes fields, down to RMS
sensitives of around 20, 22, and 32$~\mu$Jy\,beam$^{-1}$, respectively. These
fields are some of the best studied extra-galactic fields in the northern sky,
with existing deep, wide-area panchromatic photometry from X-ray to infrared
wavelengths, covering a total of $\approx$~26~\mbox{deg$^{2}$}. We first
generated improved multi-wavelength catalogues in ELAIS-N1 and Lockman Hole;
combined with the existing catalogue for Bo\"{o}tes, we present forced, matched
aperture photometry for over 7.2 million sources across the three fields. We
identified multi-wavelength counterparts to the radio detected sources, using a
combination of the Likelihood Ratio method and visual classification, which
greatly enhances the scientific potential of radio surveys and allows for the
characterisation of the photometric redshifts and the physical properties of
the host galaxies. The final radio-optical cross-matched catalogue consists of
81\,951 radio-detected sources, with counterparts identified and
multi-wavelength properties presented for 79\,820 ($>$97\%) sources. We also
examine the properties of the host galaxies, and through stacking analysis find
that the radio population with no identified counterpart is likely dominated by
AGN at $z\sim3-4$. This dataset contains one of the largest samples of
radio-selected star-forming galaxies and active galactic nuclei (AGN) at these
depths, making it ideal for studying the history of star-formation, and the
evolution of galaxies and AGN across cosmic time.
