Since I've never seen this place firsthand or even really know much about it, I'll let the professional people over at Forgotten Ohio tell you about it.
To reach Mudhouse Mansion you should take Route 22 east out of Lancaster to Lake Road. Go left on Lake Road, which winds around for about a mile, and then turn left onto Mudhouse Road. You'll be able to see the place off to the right if the corn is low and it's daytime. Otherwise you'll have to find the gated-off driveway. When I visited Mudhouse the first time I went down the driveway and parked near the house, but there's no way anyone can do that now; due to its increased popularity among local explorers, the driveway is heavily gated and plastered with bright warning signs from the Sheriff's Department. You used to be able to park behind the also-abandoned white house next to the driveway, but that burned down recently, so you'll have to be more creative than that. Be aware that if you leave your car anywhere, you'll probably regret it.
If you believe the local tales, you can take your pick. One legend tells of a government official who lived there after the Civil War and still kept slaves (in the North, even), locking them in one of the outbuildings at night. One night the slave dug his way out, entered the house, and slaughtered the entire family. Some say a more modern family was massacred there; their ghosts haunt the house. Others say it's home to the original "Bloody Mary," the ghost lady who's supposed to appear in your mirror if you say her name three or five or ten or a hundred times. Some kids in Lancaster grew up calling it the House of Mary. According to traditional American folklore, Bloody Mary's childred were killed, either by her husband or by her, and she's pissed about it. This one is tough to believe, since Bloody Mary is known all over the world, and it's pretty much a given that she never existed in the first place, much less in Fairfield County, Ohio. Then again, it's all just folklore, so you can believe just about anything you want to about Mudhouse.
So, please, check out this site and if you want, go check out the actual house if you are in the area. I don't condone trespassing or vandalism but looking at the house from a public road is definately all right. And if you have any further stories or pictures of the Mudhouse Mansion, send them in and I may post them if they're really good.