In less than 20 months, four out-of-town investment firms have become some of the largest landlords in central Ohio. Together, they have bought almost 1,300 homes, from Lancaster to Delaware, Newark to Marysville, and are adding more every week.

Four funds have bought a substantial number of houses in central Ohio.

American Homes 4 Rent, a publicly traded real-estate investment trust based in Aguora Hills, Calif., owns more than 21,000 homes nationally. Starting July 10, 2012, the company bought 728 homes in central Ohio, most of them less than 20 years old on the outskirts of the city, ranging in price from $40,100 to $238,533.

Silver Bay Realty Trust, a publicly traded firm based near Minneapolis, owns more than 6,000 homes nationally. Starting Jan. 29, 2013, the firm bought 286 homes in the Columbus area in 30- to 40-year-old suburbs, ranging in price from $33,000 to $163,000.

Magnetar Capital, a hedge fund based in Evanston, Ill., acquired 184 Westerville- and Reynoldsburg-area homes, built between 1959 and 1974, as part of 1,900 properties the firms bought from the widow of Charles Huber, a Dayton-area real-estate developer. The properties are managed by VineBrook homes, which has offices in Huber Heights, Ohio.

Mt. Helix Real Estate Investment Fund, a private investment group based in San Diego, is moving into Columbus after buying more than 1,000 homes in Indianapolis, its biggest market. Since last February, the company has bought 64 properties, most of them for less than $25,000 in distressed urban neighborhoods, and continues to add to its purchases weekly.