Cumby is a city in Hopkins County, Texas, United States.

[5] Originally known as Black Jack Grove as early as 1848, from 1857 to 1858 the post office was renamed to Theodocias.

[6] Interstate 30 runs through the south side of the city, with access from Exit 110.

[4] The city sits on a watershed divide, with the north side draining towards the South Sulphur River, part of the Red River watershed, and the south side of the city draining towards Lake Fork Creek, part of the Sabine River watershed.

According to the 2020 United States census, there were 679 people, 321 households, and 222 families residing in the city.

The city is served by the Cumby Collegiate Independent School District.