Section One of the I-35 expansion stretches from the Williamson and Bell County line to the south and US 190 in Belton to the north. The section is broken into three sections:

• Section A: Williamson/Bell County line to FM 2268 - Construction is completed.
• Section B: FM 2268 to FM 2484 in Bell County - Scheduled to be let in July 2011. The project is estimated to cost $90.4 million and will be funded through Proposition 12 bonds. A public hearing took place in March 2010.
• Section C: FM 2484 to US 190 in Belton - Scheduled to be let in April 2010 and is estimated to cost $134.8 million, funded by the American Recovery and Reinvestment Act. Schematics were presented at a public hearing on June 30, 2009 and are available for review.