comScore’s online video numbers for the US in January are out, and YouTube () is, unsurprisingly, doing great again. In January, 100.9 million visitors viewed 6.3 billion videos on the popular video sharing service, surpassing the 100 million viewers milestone in the US for the first time.

YouTube also led the large growth in online video watching, accounting for 91 percent of the incremental gain in the number of videos viewed compared to December. Fox’s MySpace () also experienced large growth: from 444 million videos viewed in December 2008 to 552 million in January 2009, with Yahoo, Viacom and Microsoft’s properties following in places three to five.

The alleged YouTube killer, Hulu (), is also growing, but at a much slower rate: from 240 million videos viewed in December 2008 to 250 million in January 2009. Hulu is still closed for most international viewers, and the lack of global buzz around the service might ultimately hamper its overall growth. If we compare the number of videos viewed, in just one month, YouTube has grown nearly two Hulus in size, so there’s a lot of catching up to do for Hulu.

See comScore’s full numbers below.