Landon Douglas Cassill (born July 7, 1989) is an American former professional stock car racing driver. He last competed full-time in the NASCAR Xfinity Series, driving the No. 10 Chevrolet Camaro for Kaulig Racing.

Cassill was born in Cedar Rapids, Iowa, and began racing on a quad when he was three years old. Cassill moved to go-karts. He finished second in the Pro Kart Tour at Atlanta Motor Speedway at the age of ten. The following year, he earned his first of two Kart Series national championships. Cassill won four International Kart Federation (IKF) championships, some on dirt and some on asphalt.

In 2000, Cassill competed in three different classes: two karting classes and a midget class. He won all three state championships on the same night. Cassill won four more state championships at the Newton Kart Klub in Newton, Iowa, in 2001. He then started racing in a modified at the half-mile Hawkeye Downs.

He was racing in the ASA Late Model Series (ASALMS) in 2003 while he was in high school at Jefferson High School in Cedar Rapids. He has also raced in legend, modified, and late model racecars. Other series include the American Speed Association and the CRA Super Series.

At age 16, he became the youngest winner in ASALMS history when he won at Lake Erie Speedway on June 9, 2006; holding the record until Erik Jones surpassed him at the age of fourteen in 2010. On July 3, Cassill won his second ASALMS race, this time in a Southern Division race at South Georgia Motorsports Park near Cecil, Georgia. The win made him the first driver to win in both the Northern and Southern Divisions. He won his first Challenge Division race at I-70 Speedway on July 8, 2010, to become the first driver to win in all three divisions. For 196 laps, Cassill held the runner-up position on the track to Peter Casilino. He secured victory by edging Casilino off the track. Answering questions afterward about the win, Cassill replied, "Hey rubbin's just racin what can I say!"

He finished second in the Challenge Division points behind Kelly Bires, and eleventh in the Northern Division despite starting in half of the races.

In 2006, Cassill was introduced to NASCAR through the GM Racing Development competition. He was one of 16 drivers that participated in the three-stage evaluation process that took place at Caraway Speedway in Asheboro, North Carolina, North Georgia Speedway in Chatsworth, Georgia, and Nashville Superspeedway.

Cassill was signed by Hendrick Motorsports in December 2006. In 2007, Cassill tested the team's Car of Tomorrow car at Lakeland Speedway and Greenville-Pickens Speedway. Along with his driving duties, Cassill has worked in the team's research and development program and drove during practices for the Hendrick pit crews. Cassill made his Nationwide Series debut at Gateway International Speedway in July 2007 after turning eighteen, as NASCAR requires national series drivers to be at least eighteen years of age (regional series drivers can be sixteen). Cassill finished 32nd in his debut. He was in contention to score his first top-ten finish at Memphis before another driver spun him out on the final lap. In his six starts that year, his best finish was eighteenth at Dover.