Casual game company Gamook has raised $1.5 million in funding from U.S. Venture Partners, Venture Beat has learned. Rick Lewis of USVP confirmed that his firm invested in the company and that he sits on its board of directors. However, Lewis said the company is in stealth mode and isn’t able to describe its operations yet. Gamook is based in Menlo Park, Calif. The company doesn’t yet have a web site.

Casual games are those that are played by mainstream consumers rather than hardcore gamers. The category is beset with competitors, from PopCap Games in casual game development to Electronic Arts’ Pogo.com casual online games site.

Venture capitalists have taken more interest in casual games recently. Hardcore games for video game consoles generate most of the industry’s revenues, but casual games have hit a $2.25 billion in revenues. Last week, Trinity Ventures invested $3.2 million in casual games company Fluid Entertainment, which is making online games for kids.

I spent a lot of time at the Casual Games Summit at the recent Game Developers Conference. Check out our coverage here.