Mathematical modeling has been positioned at the forefront of many educational levels globally because modeling reinforces purposeful problem-solving skills, connects mathematics to the real-world, and makes mathematics more meaningful and relevant. This article investigated K-12 practicing teachers' knowledge and attitudes toward mathematical modeling, while considering the relationships between them and some selected demographic variables. The study involved 335 teachers from Midwestern United States of America (U.S.), and data was collected through an Online self-administered survey. The data collected were quantitatively analyzed with the guidance of the research questions, and using statistical analyses such as correlation, multiple regression, and ANOVA. Results showed that teachers had a satisfactory knowledge and attitudes toward mathematical modeling. Teachers' knowledge of modeling was found to be positively related to their overall attitudes toward such modeling, with an R[superscript 2] = 0.25 suggesting a moderate relationship. Overall, gender and grade level band were identified as strong indicators of teachers' knowledge and attitudes toward mathematical modeling. In particular, female teachers on average showed a relatively stronger knowledge and attitudes toward mathematical modeling than their male colleagues. Similarly, elementary teachers demonstrated a relatively stronger knowledge of mathematical modeling and attitudes toward such modeling than middle or high school teachers. Findings from this study have implications for integrating mathematical modeling standards into teacher preparation programs and organizing professional development on mathematical modeling education.