We present results from a WIYN/OPTIC photometric and astrometric survey of the field of the open cluster NGC 188 ( ( l , b ) = ( 122.8° , 22.5° ) ) .
We combine these results with the proper-motion and photometry catalog of Platais et al .
and demonstrate the existence of a stellar overdensity in the background of NGC 188 .
The theoretical isochrone fits to the color-magnitude diagram of the overdensity are consistent with an age between 6 and 10 Gyr and an intermediately metal poor population ( [ Fe/H ] = -0.5 to -1.0 ) .
The distance to the overdensity is estimated to be between 10.0 and 12.6 kpc .
The proper-motions indicate that the stellar population of the overdensity is kinematically cold .

The distance estimate and the absolute proper motion of the overdensity agree reasonably well with the predictions of the Peñarrubia et al .
model of the formation of the Monoceros stream .
Orbits for this material constructed with plausible radial-velocity values , indicate that dynamically , this material is unlikely to belong to the thick disk .
Taken together , this evidence suggests that the newly-found overdensity is part of the Monoceros stream .