Large-scale native woodland loss in the Lower Rio Grande Valley of Texas during the 20th century has been reported in the literature. However, no detailed, quantitative study of landscape change in the area has been conducted. This paper presents an example of quantified native woodland loss within this area. Using historical topographic maps and aerial photographs, we were able to map the extent of native woodland areas in Cameron County in the 1930s. The historical native woodland areas were then compared with the 1983 extent of native woodlands as mapped on modern topographic quadrangles. Our results for Cameron County corroborate previous estimates of native woodlands loss in the Lower Rio Grande Valley, though at a slightly lower percentage (91%). Comparisons with recent land-use and land-cover mapping show that much of the loss was a result of agricultural expansion.