  We have conducted a survey of Faraday rotation in a sample of 191 compact
radio-loud AGNs as part of the MOJAVE (Monitoring of Jets in Active galactic
nuclei with VLBA Experiments) project. The observations were carried out with
the VLBA at 8.1, 8.4, 12.1 and 15.3 GHz over 12 epochs in 2006. We detect
sufficiently strong linear polarization in 159 out of 211 observations to
calculate the rotation measure values, resulting in a large enough sample for
statistical analysis of the Faraday rotation in blazars. These Faraday rotation
measures can be used to study the intrinsic magnetic field order and
orientation in parsec-scale blazar jets. Our sample includes 119 sources listed
in the 1FGL or 2FGL catalogs and we detect rotation measure values in 111 out
of 131 maps. Of the 72 sources that are not in the gamma-ray catalogs we detect
RM in 48 out of 80 maps. The median RM values of the LAT-detected sources do
not differ significantly from the non-LAT-detected sources. Nine of the sources
in our sample have resolved enough jets to study the transverse Faraday
rotation structure, and we detect significant transverse rotation measure
gradients in four sources. In two of these (3C~273 and 3C~454.3) there is
additional evidence to support helical magnetic field in the parsec-scale jets.
The two others (0923+392 and 2230+114) require further observations to identify
the nature of the gradient. It is interesting that three of the four sources
with significant rotation measure gradients are sources that have shown large
gamma-ray flares.
