A. J. Jernigan House, Greek Revival residence in Austin, United States.

The A. J. Jernigan House, called Las Ventanas, stands at 602 Harthan Street in west-central Austin. Master builder Abner Cook designed and built it in 1875 for the Travis County treasurer, and it was enlarged in the late 1880s and again in 1912. It is listed on the National Register of Historic Places.

The house was built in 1875 by architect Abner Cook and originally served a county official as his residence. It later underwent significant expansions and was briefly converted to office use before returning to residential purposes.

The house is also called Las Ventanas, Spanish for "the windows", a name tied to its many glazed openings. It was built in 1875 for A. J. Jernigan, then Travis County treasurer, and served as commercial office space in the late 20th century before returning to use as a single-family home around the start of the 21st century.

The house is located in an established residential neighborhood and is visible from the street, though it remains a private residence. Visitors should keep in mind it is a private property and should observe appropriate behavior when viewing it from outside.

The house is also known as Las Ventanas, Spanish for "the windows", a name not explained in the records. It was added to the National Register of Historic Places in 1983, and in the late 20th century it served as commercial office space before returning to single-family use.