Information for this annual event is now available in the events section of insaitama.com.
The Tokorozawa festival will be held on the 10th and 11th, with the main parade, music and street performances happening on the latter; Sunday the 11th.
On the 10th, most of the activities will be conducted in Motomachi community wide space 元町コミュニティ広場 from 1 to 7pm. On the 11th, the festivites will be conducted around Tokorozawa station area, from 10am to 8pm. On that day you can not drive up the main thoroughfare until after 9pm at night. Among the many things you can enjoy on the 11th, are Taiko drums and yosakoi traditional dance performances, and a parade to traditional music. There is a bazaar with booths and stalls.
The festival flyer can be viewed (japanese only) here: http://www.tokorozawa-cci.or.jp/matsuri/pamphlet/pamphlet15.pdf
The official website is http://www.tokorozawa-cci.or.jp/matsuri/index.html