Was Washington State part of Mexico?

Answer 1

No. Mexico used to own the whole states of California, Nevada, Utah, Arizona, New Mexico and Texas, as well as parts of Wyoming, Colorado, Oklahoma and Kansas.

The original US-Mexico border was defined by the Sabine River north from the Gulf of Mexico, up to the 32nd parallel north (32°N); then due north to the Red River, west along the Red River to the 100th meridian west (100°W), due north to the Arkansas River, west to its headwaters, north to the 42nd parallel north (42°N), and finally west along that parallel to the Pacific Ocean.