  We present observations and analysis of nine dwarf irregular galaxies (dIs)
in the M81 Group taken with the Advanced Camera for Surveys aboard the Hubble
Space Telescope. The nine galaxy sample (the Garland, M81 Dwarf A, DDO 53, Ho
IX, Ho I, DDO 165, NGC 2366, Ho II, and IC 2574) spans 6 magnitudes in
luminosity, a factor of 1000 in current star formation rate, and 0.5 dex in
metallicity. Here we use color-magnitude diagrams of resolved stellar
populations to study the star formation histories (SFHs) of these galaxies. We
divide the sample into faint and bright galaxies, with a dividing line of
M_${B}$ = -15, and then analyze the similarities and differences in the SFHs,
birthrate parameters, fraction of stars formed per time interval, and spatial
distribution of stellar components. Comparing these parameters as a function of
luminosity, we find only minor differences in SF characteristics. We extend our
comparison to select dIs in the Local Group (LG), and find only minor
differences in SF parameters. The fraction of stars formed per time interval
for an average M81 Group and LG dI is consistent with a constant SFH. However,
individual galaxies can show significant departures from a constant SFH. Thus,
we find this result underlines the importance of stochastic SF in dIs. We also
compare possible formation scenarios of the less luminous and candidate tidal
dwarfs in the M81 Group. The SFHs and the lack of an overdensity of associated
red stars suggest that the Garland and Ho IX are not dIs and are potentially
tidal dwarf galaxies. Interestingly, a noteworthy difference between the LG and
the M81 Group is the lack of tidal dwarf candidates in the LG.
