Waco ( WAY-koh) is a city in central Texas and is the county seat of McLennan County, Texas, United States. It is situated along the Brazos River and I-35, halfway between Dallas and Austin. The city had a 2010 population of 124,805, making it the 22nd-most populous city in the state. The 2017 US Census population estimate is 136,436 The Waco Metropolitan Statistical Area consists of McLennan and Falls Counties, which had a 2010 population of 234,906. Falls County was added to the Waco MSA in 2013. The 2017 US Census population estimate for the Waco MSA is 268,696.