The Hill Reports that there is yet another service tracking government tweets:
The site is GovLive , which aggregates "all government news releases in one place" and aims to "be the first comprehensive search engine for finding local government news in real-time." Its tweets page  gives a real-time "bird's-eye view of official government Twitter feeds across the US" and allows you to filter by State or County!
The Hill says GovLive tracks 68,031 tweets from 540 agencies.
Other services that are tracking government tweets include: