When it was originally established in 1890 , it was known as E County ( several Oklahoma counties carried only letter designations at the time ) .
Day County was in the western part of the territory , along the Texas border .
When Day County was originally established in 1890 , Day County was known as E County ( several Oklahoma counties carried only letter designations at the time ) .
Day County was in the western part of the territory , along the Texas border .