Sienna, formerly known as Sienna Plantation, is a census-designated place and master-planned community located in Fort Bend County, Texas, United States. It is mostly in the extraterritorial jurisdiction (ETJ) of Missouri City with the remainder in the ETJ of Arcola. The population was 20,204 at the 2020 census, up from 13,721 at the 2010 census.

Fort Bend County is a county located in the U.S. state of Texas. The county was founded in 1837 and organized the next year. It is named for a blockhouse at a bend of the Brazos River. The community developed around the fort in early days. The county seat is Richmond. The largest city located entirely within the county borders is Sugar Land. The largest city by population in the county is Houston; however, most of Houston's population is located in neighboring Harris County.