Lewisville Lake is on the Elm Fork of the Trinity River one mile northeast of Lewisville and fifteen miles southeast of Denton in southeastern Denton County. The reservoir is owned by the United States government and operated by the United States Army Corps of Engineers, Fort Worth District; its purpose is to control potential flood waters originating within the Elm Fork drainage basin. In addition, the lake assists in soil conservation, serves as a recreational area, and provides water for local municipalities.
Lewisville Lake is the second water-storage reservoir to impound the waters of the Elm Fork on this site. The first facility, Lake Dallas, served for thirty-one years as the principal source of municipal water for its owner, the city of Dallas. Construction of this lake, with its eighty-foot-high, 11,000-foot-long dam located near the village of Garza (renamed Lake Dallas, Texas, in 1929), began in February 1928. The lake was built by the W. E. Callahan Construction Company at a cost of just over $3 million. It had a 194,000-acre-foot capacity at an elevation of 525 feet and covered over 10,000 acres. It was nine miles long and three miles wide and had a forty-three-mile shoreline.
As flood control and conservation became more serious issues in the 1940s, Congress responded by passing the River and Harbor Act of March 2, 1945, which called for the construction of four flood-control lakes within the Trinity River basin. On November 28, 1948, the Corps of Engineers began work on a new Denton County dam and lake that would impound the waters of Clear, Little Elm, Stewart, Pecan, and Hickory creeks in addition to those of the Trinity River's Elm Fork. Although the 125-foot-high and 33,000-foot-long dam was not completed until 1955, impoundment began on November 1, 1954. The total cost of this project, known originally as the Garza-Little Elm Reservoir and Dam, was $21,756,500, with the cities of Dallas, Highland Park, University Park, and Denton contributing to the cost in exchange for access to the water. The new reservoir, popularly called Garza-Little Elm Lake, incorporated the older and smaller Lake Dallas on October 28, 1957, when the old Garza Dam was breached. The huge lake that resulted was thirteen miles long, had a 183-mile shoreline and a capacity of 436,000 acre-feet at an elevation of 515 feet, and covered almost one-fifth of Denton County.
The joining of Lake Dallas and Garza-Little Elm Reservoir apparently led to confusion concerning the facility's legal name, a problem which was compounded when the government redesignated the dam as Lewisville Dam in 1955 and the lake as Lewisville Reservoir in 1960. However, the decision concerning the lake's name was reversed the following year. Garza-Little Elm Reservoir remained the lake's official title until the mid-1970s, when it was renamed Lewisville Lake.