  The finding of active galactic nuclei (AGN) in dwarf galaxies has important
implications for galaxy evolution and supermassive black hole formation models.
Yet, how AGN in dwarf galaxies form is still debated, in part due to scant
demographics. We make use of the MaNGA survey, comprising $\sim$10,000 galaxies
at z $<$ 0.15, to identify AGN dwarf galaxies using a spaxel by spaxel
classification in three spatially-resolved emission line diagnostic diagrams
(the [NII-, [SII]- and [OI]-BPT) and the WHAN diagram. This yields a sample of
664 AGN dwarf galaxies, the largest to date, and an AGN fraction of $\sim20\%$
that is significantly larger than that of single-fiber-spectroscopy studies
(i.e. $\sim1\%$). This can be explained by the lower bolometric luminosity ($<
10^{42}$ erg s$^{-1}$) and accretion rate (sub-Eddington) of the MaNGA AGN
dwarf galaxies. We additionally identify 1,176 SF-AGN (classified as
star-forming in the [NII]-BPT but as AGN in the [SII]- and [OI]-BPT), 122
Composite, and 173 LINER sources. The offset between the optical center of the
galaxy and the median position of the AGN spaxels is more than 3 arcsec for
$\sim$62\% of the AGN, suggesting that some could be off-nuclear. We also
identify seven new broad-line AGN with log $M_\mathrm{BH}$ = 5.0 - 5.9
$M_\mathrm{\odot}$. Our results show how integral-field spectroscopy is a
powerful tool for uncovering faint and low-accretion AGN and better
constraining the demographics of AGN in dwarf galaxies.
