Which Western state or territory was the first to officially forbid black

children from attending the same schools as white children

Indianapolis

Explanation:

In 1920s, the authorities not only in the South, but also in the West also moved to tighten segregation policy. When Blacks began to move in large numbers to Indiana cities in the 1920s, the white population reacted with a policy of restrictions (i. e., segregation). By 1929, Indianapolis schools were completely segregated. Not all northern cities have policies similar to Indianapolis. Some cities, like Chicago, officially avoided segregation, but schools were de facto segregated.