It grew rapidly after this and supposedly reached a peak population of about 1,500 people in 1886, although this claim is called into question by figures from the 1880 census, when the town had only 173 residents. If, indeed, the town grew by over 1,300 people in the first six years of the 1880s, it must have lost residents in the latter half of the decade almost as fast it had gained them in the first half, because the estimated population in 1890 was only 707.
In 1912, when a Springfield newspaperman visited Southwest City, he estimated the town's population at about 800, although this figure is also belied by the official census just two years earlier when the town's population was only 483.
At the time of the reporter's visit, Southwest City was serviced by a branch of the Frisco Railroad that ran from Rogers, Arkansas, to Grove, Oklahoma. The town had three churches and a high school (a two-story brick structure built in 1896). Among the town's businesses were a bank, a hotel, a newspaper, a hardware and implement store, a lumber company, a dry goods store, and a drugstore. Southwest City likely also had several general stores, but the newspaperman failed to mention them. Fruit growing and the poultry industry were also going strong in the area. (The poultry processing plant at Southwest City today is one of the largest employers in McDonald County.)
Southwest City's population remained pretty steady in the 400-600 range throughout most of the 20th century. Starting about 1990, it enjoyed a modest growth spurt for the next twenty years, with its population peaking at 970 in 2010. The 2020 population stood at 922.