DEERFIELD, Ill. — Walgreen Co. reported December sales rose 10.1 percent to $1 billion, the first billion-dollar sales month in its history. Comparable store sales rose 4 percent for the month. The company reported first-quarter earnings in fiscal 1994 rose 11.6 percent, to $44.2 million, or 36 cents a share.

In the quarter ended Nov. 30, sales rose 10.6 percent, to $2.1 billion from $1.9 billion. Comparable store sales were up 5.3 percent, despite no raise in prices of pharmaceuticals and general merchandise, the firm said. In the first quarter of fiscal 1993, the company earned $39.6 million, or 32 cents, before an accounting charge. A $23.6 million fee for post-retirement benefits and income tax changes reduced net earnings to $16 million, or 13 cents.

Charles R. Walgreen 3rd, Walgreen’s chairman, said the company’s “aggressive expansion plans are very much on schedule,” with 63 stores opened in the quarter, compared with 36 stores in the comparable period last year.

Walgreen opened 149 stores in fiscal 1993 and plans to open 175 drugstores in fiscal 1994. L. Daniel Jorndt, president, said the firm will expand into Cleveland and Buffalo next year and will open 200 new stores nationwide by 1996.

As of Dec. 31, Walgreen operated 1,892 stores in 30 states and Puerto Rico, up from 1,761 a year ago.